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 $53.41   12.252%   $59.9538   $59.95   $59.95   $60.00  
  Purchase #2 $109.96   7.244%   $117.9255   $117.93   $117.95   $117.90  
  Purchase #3 $243.92   9.874%   $268.0047   $268.00   $268.00   $268.00  
  Purchase #4 $16.99   12.275%   $19.0755   $19.08   $19.10   $19.10  
  Purchase #5 $10.88   13.710%   $12.3716   $12.37   $12.35   $12.40  
  Purchase #6 $244.31   6.424%   $260.0045   $260.00   $260.00   $260.00  
  Purchase #7 $79.93   11.329%   $88.9853   $88.99   $89.00   $89.00  
  7 purchase totals = $759.40       $826.3209   $826.32   $826.35   $826.40