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 $53.64   11.181%   $59.6375   $59.64   $59.65   $59.60  
  Purchase #2 $173.99   11.319%   $193.6839   $193.68   $193.70   $193.70  
  Purchase #3 $104.26   6.122%   $110.6428   $110.64   $110.65   $110.60  
  Purchase #4 $61.78   6.525%   $65.8111   $65.81   $65.80   $65.80  
  Purchase #5 $49.84   9.740%   $54.6944   $54.69   $54.70   $54.70  
  Purchase #6 $191.78   12.782%   $216.2933   $216.29   $216.30   $216.30  
  Purchase #7 $219.56   11.122%   $243.9795   $243.98   $244.00   $244.00  
  7 purchase totals = $854.85       $944.7425   $944.73   $944.80   $944.70