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 $61.99   4.810%   $64.9717   $64.97   $64.95   $65.00  
  Purchase #2 $99.64   3.684%   $103.3107   $103.31   $103.30   $103.30  
  Purchase #3 $134.82   10.585%   $149.0907   $149.09   $149.10   $149.10  
  Purchase #4 $150.77   5.840%   $159.575   $159.58   $159.60   $159.60  
  Purchase #5 $77.70   8.714%   $84.4708   $84.47   $84.45   $84.50  
  Purchase #6 $17.83   12.594%   $20.0755   $20.08   $20.10   $20.10  
  Purchase #7 $226.34   6.689%   $241.4799   $241.48   $241.50   $241.50  
  7 purchase totals = $769.09       $822.9743   $822.98   $823.00   $823.10