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 $59.75   13.278%   $67.6836   $67.68   $67.70   $67.70  
  Purchase #2 $180.70   10.836%   $200.2807   $200.28   $200.30   $200.30  
  Purchase #3 $124.93   5.820%   $132.2009   $132.20   $132.20   $132.20  
  Purchase #4 $25.95   10.725%   $28.7331   $28.73   $28.75   $28.70  
  Purchase #5 $150.33   10.333%   $165.8636   $165.86   $165.85   $165.90  
  Purchase #6 $216.80   9.109%   $236.5483   $236.55   $236.55   $236.50  
  Purchase #7 $220.84   3.819%   $229.2739   $229.27   $229.25   $229.30  
  7 purchase totals = $979.30       $1,060.5841   $1,060.57   $1,060.60   $1,060.60