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 $30.65   6.869%   $32.7553   $32.76   $32.75   $32.80  
  Purchase #2 $150.79   9.217%   $164.6883   $164.69   $164.70   $164.70  
  Purchase #3 $50.72   6.566%   $54.0503   $54.05   $54.05   $54.10  
  Purchase #4 $214.77   10.772%   $237.905   $237.91   $237.90   $237.90  
  Purchase #5 $245.78   3.188%   $253.6155   $253.62   $253.60   $253.60  
  Purchase #6 $110.96   6.350%   $118.006   $118.01   $118.00   $118.00  
  Purchase #7 $133.95   10.460%   $147.9612   $147.96   $147.95   $148.00  
  7 purchase totals = $937.62       $1,008.9816   $1,009.00   $1,008.95   $1,009.10