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 $148.91   12.773%   $167.9303   $167.93   $167.95   $167.90  
  Purchase #2 $137.82   7.637%   $148.3453   $148.35   $148.35   $148.30  
  Purchase #3 $241.77   8.461%   $262.2262   $262.23   $262.25   $262.20  
  Purchase #4 $38.88   11.785%   $43.462   $43.46   $43.45   $43.50  
  Purchase #5 $62.88   3.289%   $64.9481   $64.95   $64.95   $64.90  
  Purchase #6 $117.55   7.143%   $125.9466   $125.95   $125.95   $125.90  
  Purchase #7 $56.40   12.854%   $63.6497   $63.65   $63.65   $63.60  
  7 purchase totals = $804.21       $876.5082   $876.52   $876.55   $876.30