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 $202.35   11.841%   $226.3103   $226.31   $226.30   $226.30  
  Purchase #2 $203.73   3.344%   $210.5427   $210.54   $210.55   $210.50  
  Purchase #3 $105.96   10.126%   $116.6895   $116.69   $116.70   $116.70  
  Purchase #4 $134.62   5.207%   $141.6297   $141.63   $141.65   $141.60  
  Purchase #5 $227.82   11.385%   $253.7573   $253.76   $253.75   $253.80  
  Purchase #6 $77.52   8.827%   $84.3627   $84.36   $84.35   $84.40  
  Purchase #7 $147.79   13.733%   $168.086   $168.09   $168.10   $168.10  
  7 purchase totals = $1,099.79       $1,201.3782   $1,201.38   $1,201.40   $1,201.40