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 $60.54   7.312%   $64.9667   $64.97   $64.95   $65.00  
  Purchase #2 $242.67   4.679%   $254.0245   $254.02   $254.00   $254.00  
  Purchase #3 $55.53   7.443%   $59.6631   $59.66   $59.65   $59.70  
  Purchase #4 $235.43   10.568%   $260.3102   $260.31   $260.30   $260.30  
  Purchase #5 $38.41   3.227%   $39.6495   $39.65   $39.65   $39.60  
  Purchase #6 $88.46   6.813%   $94.4868   $94.49   $94.50   $94.50  
  Purchase #7 $130.84   5.723%   $138.328   $138.33   $138.35   $138.30  
  7 purchase totals = $851.88       $911.4288   $911.43   $911.40   $911.40