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 $208.54   11.296%   $232.0967   $232.10   $232.10   $232.10  
  Purchase #2 $245.30   3.835%   $254.7073   $254.71   $254.70   $254.70  
  Purchase #3 $85.88   6.287%   $91.2793   $91.28   $91.30   $91.30  
  Purchase #4 $44.31   9.746%   $48.6285   $48.63   $48.65   $48.60  
  Purchase #5 $62.84   12.772%   $70.8659   $70.87   $70.85   $70.90  
  Purchase #6 $20.68   9.233%   $22.5894   $22.59   $22.60   $22.60  
  Purchase #7 $80.74   6.813%   $86.2408   $86.24   $86.25   $86.20  
  7 purchase totals = $748.29       $806.4079   $806.42   $806.45   $806.40