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 $56.96   10.233%   $62.7887   $62.79   $62.80   $62.80  
  Purchase #2 $198.32   9.261%   $216.6864   $216.69   $216.70   $216.70  
  Purchase #3 $88.26   4.814%   $92.5088   $92.51   $92.50   $92.50  
  Purchase #4 $58.35   6.677%   $62.246   $62.25   $62.25   $62.20  
  Purchase #5 $102.54   9.731%   $112.5182   $112.52   $112.50   $112.50  
  Purchase #6 $250.98   6.848%   $268.1671   $268.17   $268.15   $268.20  
  Purchase #7 $146.42   9.379%   $160.1527   $160.15   $160.15   $160.20  
  7 purchase totals = $901.83       $975.0679   $975.08   $975.05   $975.10