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 $82.93   10.851%   $91.9287   $91.93   $91.95   $91.90  
  Purchase #2 $22.44   5.820%   $23.746   $23.75   $23.75   $23.70  
  Purchase #3 $183.28   7.709%   $197.4091   $197.41   $197.40   $197.40  
  Purchase #4 $43.90   12.211%   $49.2606   $49.26   $49.25   $49.30  
  Purchase #5 $212.30   12.361%   $238.5424   $238.54   $238.55   $238.50  
  Purchase #6 $183.52   3.204%   $189.4   $189.40   $189.40   $189.40  
  Purchase #7 $75.56   8.496%   $81.9796   $81.98   $82.00   $82.00  
  7 purchase totals = $803.93       $872.2664   $872.27   $872.30   $872.20