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 $23.44   8.871%   $25.5194   $25.52   $25.50   $25.50  
  Purchase #2 $225.33   7.373%   $241.9436   $241.94   $241.95   $241.90  
  Purchase #3 $194.37   8.550%   $210.9886   $210.99   $211.00   $211.00  
  Purchase #4 $64.49   6.427%   $68.6348   $68.63   $68.65   $68.60  
  Purchase #5 $59.32   11.555%   $66.1744   $66.17   $66.15   $66.20  
  Purchase #6 $13.38   12.798%   $15.0924   $15.09   $15.10   $15.10  
  Purchase #7 $184.77   12.248%   $207.4006   $207.40   $207.40   $207.40  
  7 purchase totals = $765.10       $835.7538   $835.74   $835.75   $835.70