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 $214.37   6.603%   $228.5249   $228.52   $228.50   $228.50  
  Purchase #2 $58.52   5.808%   $61.9188   $61.92   $61.90   $61.90  
  Purchase #3 $71.86   5.471%   $75.7915   $75.79   $75.80   $75.80  
  Purchase #4 $119.60   5.782%   $126.5153   $126.52   $126.50   $126.50  
  Purchase #5 $230.48   5.496%   $243.1472   $243.15   $243.15   $243.10  
  Purchase #6 $62.32   3.489%   $64.4943   $64.49   $64.50   $64.50  
  Purchase #7 $164.80   12.657%   $185.6587   $185.66   $185.65   $185.70  
  7 purchase totals = $921.95       $986.0507   $986.05   $986.00   $986.00