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 $23.45   8.492%   $25.4414   $25.44   $25.45   $25.40  
  Purchase #2 $22.84   10.334%   $25.2003   $25.20   $25.20   $25.20  
  Purchase #3 $33.64   5.675%   $35.5491   $35.55   $35.55   $35.50  
  Purchase #4 $92.44   9.231%   $100.9731   $100.97   $100.95   $101.00  
  Purchase #5 $219.62   11.779%   $245.489   $245.49   $245.50   $245.50  
  Purchase #6 $238.85   5.192%   $251.2511   $251.25   $251.25   $251.30  
  Purchase #7 $67.77   5.662%   $71.6071   $71.61   $71.60   $71.60  
  7 purchase totals = $698.61       $755.5111   $755.51   $755.50   $755.50