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 $117.73   11.344%   $131.0853   $131.09   $131.10   $131.10  
  Purchase #2 $60.62   13.759%   $68.9607   $68.96   $68.95   $69.00  
  Purchase #3 $149.31   7.175%   $160.023   $160.02   $160.00   $160.00  
  Purchase #4 $161.92   12.672%   $182.4385   $182.44   $182.45   $182.40  
  Purchase #5 $120.80   3.504%   $125.0328   $125.03   $125.05   $125.00  
  Purchase #6 $207.44   13.141%   $234.6997   $234.70   $234.70   $234.70  
  Purchase #7 $44.51   8.640%   $48.3557   $48.36   $48.35   $48.40  
  7 purchase totals = $862.33       $950.5957   $950.60   $950.60   $950.60