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 $23.96   8.277%   $25.9432   $25.94   $25.95   $25.90  
  Purchase #2 $142.81   11.791%   $159.6487   $159.65   $159.65   $159.60  
  Purchase #3 $214.81   5.125%   $225.819   $225.82   $225.80   $225.80  
  Purchase #4 $187.27   13.611%   $212.7593   $212.76   $212.75   $212.80  
  Purchase #5 $172.32   4.224%   $179.5988   $179.60   $179.60   $179.60  
  Purchase #6 $6.46   11.599%   $7.2093   $7.21   $7.20   $7.20  
  Purchase #7 $235.78   9.821%   $258.936   $258.94   $258.95   $258.90  
  7 purchase totals = $983.41       $1,069.9143   $1,069.92   $1,069.90   $1,069.80