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 $221.59   10.489%   $244.8326   $244.83   $244.85   $244.80  
  Purchase #2 $68.97   11.171%   $76.6746   $76.67   $76.65   $76.70  
  Purchase #3 $111.42   4.422%   $116.347   $116.35   $116.35   $116.30  
  Purchase #4 $18.87   8.526%   $20.4789   $20.48   $20.50   $20.50  
  Purchase #5 $121.59   11.297%   $135.326   $135.33   $135.35   $135.30  
  Purchase #6 $156.82   3.270%   $161.948   $161.95   $161.95   $161.90  
  Purchase #7 $35.95   13.323%   $40.7396   $40.74   $40.75   $40.70  
  7 purchase totals = $735.21       $796.3467   $796.35   $796.40   $796.20