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 $144.77   12.864%   $163.3932   $163.39   $163.40   $163.40  
  Purchase #2 $43.57   7.176%   $46.6966   $46.70   $46.70   $46.70  
  Purchase #3 $167.78   5.752%   $177.4307   $177.43   $177.45   $177.40  
  Purchase #4 $56.38   8.562%   $61.2073   $61.21   $61.20   $61.20  
  Purchase #5 $56.32   6.107%   $59.7595   $59.76   $59.75   $59.80  
  Purchase #6 $146.78   8.596%   $159.3972   $159.40   $159.40   $159.40  
  Purchase #7 $83.83   12.350%   $94.183   $94.18   $94.20   $94.20  
  7 purchase totals = $699.43       $762.0675   $762.07   $762.10   $762.10