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 $61.82   7.269%   $66.3137   $66.31   $66.30   $66.30  
  Purchase #2 $230.92   9.581%   $253.0444   $253.04   $253.05   $253.00  
  Purchase #3 $86.86   12.626%   $97.8269   $97.83   $97.85   $97.80  
  Purchase #4 $117.75   4.375%   $122.9016   $122.90   $122.90   $122.90  
  Purchase #5 $81.36   3.651%   $84.3305   $84.33   $84.35   $84.30  
  Purchase #6 $177.79   9.601%   $194.8596   $194.86   $194.85   $194.90  
  Purchase #7 $223.92   3.584%   $231.9453   $231.95   $231.95   $231.90  
  7 purchase totals = $980.42       $1,051.2220   $1,051.22   $1,051.25   $1,051.10