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 $61.48   9.731%   $67.4626   $67.46   $67.45   $67.50  
  Purchase #2 $165.31   8.730%   $179.7416   $179.74   $179.75   $179.70  
  Purchase #3 $232.35   4.688%   $243.2426   $243.24   $243.25   $243.20  
  Purchase #4 $12.68   13.427%   $14.3825   $14.38   $14.40   $14.40  
  Purchase #5 $57.47   5.364%   $60.5527   $60.55   $60.55   $60.60  
  Purchase #6 $28.64   6.559%   $30.5185   $30.52   $30.50   $30.50  
  Purchase #7 $26.97   4.494%   $28.182   $28.18   $28.20   $28.20  
  7 purchase totals = $584.90       $624.0825   $624.07   $624.10   $624.10