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 $212.73   10.146%   $234.3136   $234.31   $234.30   $234.30  
  Purchase #2 $35.56   6.747%   $37.9592   $37.96   $37.95   $38.00  
  Purchase #3 $247.82   11.538%   $276.4135   $276.41   $276.40   $276.40  
  Purchase #4 $177.50   13.794%   $201.9844   $201.98   $202.00   $202.00  
  Purchase #5 $107.99   10.177%   $118.9801   $118.98   $119.00   $119.00  
  Purchase #6 $137.79   4.397%   $143.8486   $143.85   $143.85   $143.80  
  Purchase #7 $10.59   6.785%   $11.3085   $11.31   $11.30   $11.30  
  7 purchase totals = $929.98       $1,024.8079   $1,024.80   $1,024.80   $1,024.80