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 $59.68   8.278%   $64.6203   $64.62   $64.60   $64.60  
  Purchase #2 $204.51   13.415%   $231.945   $231.95   $231.95   $231.90  
  Purchase #3 $16.32   3.621%   $16.9109   $16.91   $16.90   $16.90  
  Purchase #4 $71.63   6.179%   $76.056   $76.06   $76.05   $76.10  
  Purchase #5 $25.58   4.343%   $26.6909   $26.69   $26.70   $26.70  
  Purchase #6 $218.86   3.355%   $226.2028   $226.20   $226.20   $226.20  
  Purchase #7 $57.79   8.483%   $62.6923   $62.69   $62.70   $62.70  
  7 purchase totals = $654.37       $705.1182   $705.12   $705.10   $705.10