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 $214.26   5.781%   $226.6464   $226.65   $226.65   $226.60  
  Purchase #2 $220.73   7.474%   $237.2274   $237.23   $237.25   $237.20  
  Purchase #3 $173.29   8.637%   $188.2571   $188.26   $188.25   $188.30  
  Purchase #4 $22.60   12.203%   $25.3579   $25.36   $25.35   $25.40  
  Purchase #5 $39.29   10.194%   $43.2952   $43.30   $43.30   $43.30  
  Purchase #6 $244.95   7.754%   $263.9434   $263.94   $263.95   $263.90  
  Purchase #7 $83.97   13.347%   $95.1775   $95.18   $95.20   $95.20  
  7 purchase totals = $999.09       $1,079.9049   $1,079.92   $1,079.95   $1,079.90