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 $208.62   8.146%   $225.6142   $225.61   $225.60   $225.60  
  Purchase #2 $61.75   7.303%   $66.2596   $66.26   $66.25   $66.30  
  Purchase #3 $65.50   13.254%   $74.1814   $74.18   $74.20   $74.20  
  Purchase #4 $34.54   12.157%   $38.739   $38.74   $38.75   $38.70  
  Purchase #5 $43.94   4.214%   $45.7916   $45.79   $45.80   $45.80  
  Purchase #6 $61.73   5.313%   $65.0097   $65.01   $65.00   $65.00  
  Purchase #7 $241.56   3.687%   $250.4663   $250.47   $250.45   $250.50  
  7 purchase totals = $717.64       $766.0618   $766.06   $766.05   $766.10