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 $61.68   7.462%   $66.2826   $66.28   $66.30   $66.30  
  Purchase #2 $141.41   6.746%   $150.9495   $150.95   $150.95   $150.90  
  Purchase #3 $128.61   10.747%   $142.4317   $142.43   $142.45   $142.40  
  Purchase #4 $163.37   9.559%   $178.9865   $178.99   $179.00   $179.00  
  Purchase #5 $60.57   8.312%   $65.6046   $65.60   $65.60   $65.60  
  Purchase #6 $44.79   8.468%   $48.5828   $48.58   $48.60   $48.60  
  Purchase #7 $56.91   8.393%   $61.6865   $61.69   $61.70   $61.70  
  7 purchase totals = $657.34       $714.5242   $714.52   $714.60   $714.50