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 $23.44   5.170%   $24.6518   $24.65   $24.65   $24.70  
  Purchase #2 $222.73   3.266%   $230.0044   $230.00   $230.00   $230.00  
  Purchase #3 $204.85   11.124%   $227.6375   $227.64   $227.65   $227.60  
  Purchase #4 $170.74   10.224%   $188.1965   $188.20   $188.20   $188.20  
  Purchase #5 $150.97   5.388%   $159.1043   $159.10   $159.10   $159.10  
  Purchase #6 $82.59   11.357%   $91.9697   $91.97   $91.95   $92.00  
  Purchase #7 $98.68   9.172%   $107.7309   $107.73   $107.75   $107.70  
  7 purchase totals = $954.00       $1,029.2951   $1,029.29   $1,029.30   $1,029.30