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 $91.52   6.581%   $97.5429   $97.54   $97.55   $97.50  
  Purchase #2 $104.44   11.705%   $116.6647   $116.66   $116.65   $116.70  
  Purchase #3 $170.67   8.251%   $184.752   $184.75   $184.75   $184.80  
  Purchase #4 $31.93   6.352%   $33.9582   $33.96   $33.95   $34.00  
  Purchase #5 $48.44   13.144%   $54.807   $54.81   $54.80   $54.80  
  Purchase #6 $39.94   12.562%   $44.9573   $44.96   $44.95   $45.00  
  Purchase #7 $169.43   3.217%   $174.8806   $174.88   $174.90   $174.90  
  7 purchase totals = $656.37       $707.5627   $707.56   $707.55   $707.70