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 $235.56   13.455%   $267.2546   $267.25   $267.25   $267.30  
  Purchase #2 $108.58   6.438%   $115.5704   $115.57   $115.55   $115.60  
  Purchase #3 $101.93   12.800%   $114.977   $114.98   $115.00   $115.00  
  Purchase #4 $49.90   4.703%   $52.2468   $52.25   $52.25   $52.20  
  Purchase #5 $56.47   12.865%   $63.7349   $63.73   $63.75   $63.70  
  Purchase #6 $127.71   5.320%   $134.5042   $134.50   $134.50   $134.50  
  Purchase #7 $123.94   7.727%   $133.5168   $133.52   $133.50   $133.50  
  7 purchase totals = $804.09       $881.8047   $881.80   $881.80   $881.80