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 $209.46   3.470%   $216.7283   $216.73   $216.75   $216.70  
  Purchase #2 $230.95   12.368%   $259.5139   $259.51   $259.50   $259.50  
  Purchase #3 $60.67   5.849%   $64.2186   $64.22   $64.20   $64.20  
  Purchase #4 $29.92   9.461%   $32.7507   $32.75   $32.75   $32.80  
  Purchase #5 $24.63   11.744%   $27.5225   $27.52   $27.50   $27.50  
  Purchase #6 $29.78   13.227%   $33.719   $33.72   $33.70   $33.70  
  Purchase #7 $128.95   3.354%   $133.275   $133.28   $133.30   $133.30  
  7 purchase totals = $714.36       $767.7280   $767.73   $767.70   $767.70