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 $85.31   13.417%   $96.756   $96.76   $96.75   $96.80  
  Purchase #2 $151.70   12.404%   $170.5169   $170.52   $170.50   $170.50  
  Purchase #3 $247.78   10.182%   $273.009   $273.01   $273.00   $273.00  
  Purchase #4 $22.69   13.154%   $25.6746   $25.67   $25.65   $25.70  
  Purchase #5 $39.92   3.214%   $41.203   $41.20   $41.20   $41.20  
  Purchase #6 $140.78   12.791%   $158.7872   $158.79   $158.80   $158.80  
  Purchase #7 $238.69   10.119%   $262.843   $262.84   $262.85   $262.80  
  7 purchase totals = $926.87       $1,028.7897   $1,028.79   $1,028.75   $1,028.80