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 $61.36   3.351%   $63.4162   $63.42   $63.40   $63.40  
  Purchase #2 $12.78   7.233%   $13.7044   $13.70   $13.70   $13.70  
  Purchase #3 $71.89   3.627%   $74.4975   $74.50   $74.50   $74.50  
  Purchase #4 $226.57   3.684%   $234.9168   $234.92   $234.90   $234.90  
  Purchase #5 $149.87   12.221%   $168.1856   $168.19   $168.20   $168.20  
  Purchase #6 $247.31   11.316%   $275.2956   $275.30   $275.30   $275.30  
  Purchase #7 $124.44   6.587%   $132.6369   $132.64   $132.65   $132.60  
  7 purchase totals = $894.22       $962.6530   $962.67   $962.65   $962.60