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 $192.47   4.306%   $200.7578   $200.76   $200.75   $200.80  
  Purchase #2 $101.55   11.289%   $113.014   $113.01   $113.00   $113.00  
  Purchase #3 $15.28   11.488%   $17.0354   $17.04   $17.05   $17.00  
  Purchase #4 $39.81   6.253%   $42.2993   $42.30   $42.30   $42.30  
  Purchase #5 $63.38   3.331%   $65.4912   $65.49   $65.50   $65.50  
  Purchase #6 $206.92   11.317%   $230.3371   $230.34   $230.35   $230.30  
  Purchase #7 $69.88   10.246%   $77.0399   $77.04   $77.05   $77.00  
  7 purchase totals = $689.29       $745.9747   $745.98   $746.00   $745.90