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 $224.41   9.282%   $245.2397   $245.24   $245.25   $245.20  
  Purchase #2 $231.78   10.591%   $256.3278   $256.33   $256.35   $256.30  
  Purchase #3 $87.94   6.846%   $93.9604   $93.96   $93.95   $94.00  
  Purchase #4 $71.77   5.429%   $75.6664   $75.67   $75.65   $75.70  
  Purchase #5 $104.88   8.661%   $113.9637   $113.96   $113.95   $114.00  
  Purchase #6 $228.73   6.570%   $243.7576   $243.76   $243.75   $243.80  
  Purchase #7 $123.52   7.817%   $133.1756   $133.18   $133.20   $133.20  
  7 purchase totals = $1,073.03       $1,162.0912   $1,162.10   $1,162.10   $1,162.20