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 $95.68   13.674%   $108.7633   $108.76   $108.75   $108.80  
  Purchase #2 $224.96   11.731%   $251.3501   $251.35   $251.35   $251.40  
  Purchase #3 $182.94   3.124%   $188.655   $188.66   $188.65   $188.70  
  Purchase #4 $75.63   11.439%   $84.2813   $84.28   $84.30   $84.30  
  Purchase #5 $97.96   9.762%   $107.5229   $107.52   $107.50   $107.50  
  Purchase #6 $185.27   8.295%   $200.6381   $200.64   $200.65   $200.60  
  Purchase #7 $235.51   8.524%   $255.5849   $255.58   $255.60   $255.60  
  7 purchase totals = $1,097.95       $1,196.7956   $1,196.79   $1,196.80   $1,196.90