Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.98   10.615%   $261.0293   $261.03   $261.05   $261.00  
  Purchase #2 $127.82   7.803%   $137.7938   $137.79   $137.80   $137.80  
  Purchase #3 $188.42   11.237%   $209.5928   $209.59   $209.60   $209.60  
  Purchase #4 $120.82   12.266%   $135.6398   $135.64   $135.65   $135.60  
  Purchase #5 $189.76   6.441%   $201.9824   $201.98   $202.00   $202.00  
  Purchase #6 $182.82   12.871%   $206.3508   $206.35   $206.35   $206.40  
  Purchase #7 $107.62   7.386%   $115.5688   $115.57   $115.55   $115.60  
  7 purchase totals = $1,153.24       $1,267.9577   $1,267.95   $1,268.00   $1,268.00