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 $78.88   12.622%   $88.8362   $88.84   $88.85   $88.80  
  Purchase #2 $102.71   9.692%   $112.6647   $112.66   $112.65   $112.70  
  Purchase #3 $31.43   11.185%   $34.9454   $34.95   $34.95   $34.90  
  Purchase #4 $167.41   6.822%   $178.8307   $178.83   $178.85   $178.80  
  Purchase #5 $114.76   10.363%   $126.6526   $126.65   $126.65   $126.70  
  Purchase #6 $120.44   12.419%   $135.3974   $135.40   $135.40   $135.40  
  Purchase #7 $249.56   13.393%   $282.9836   $282.98   $283.00   $283.00  
  7 purchase totals = $865.19       $960.3106   $960.31   $960.35   $960.30