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 $24.98   5.592%   $26.3769   $26.38   $26.40   $26.40  
  Purchase #2 $159.30   10.392%   $175.8545   $175.85   $175.85   $175.90  
  Purchase #3 $22.87   3.776%   $23.7336   $23.73   $23.75   $23.70  
  Purchase #4 $91.78   11.489%   $102.3246   $102.32   $102.30   $102.30  
  Purchase #5 $78.61   7.795%   $84.7376   $84.74   $84.75   $84.70  
  Purchase #6 $109.62   10.382%   $121.0007   $121.00   $121.00   $121.00  
  Purchase #7 $152.47   6.162%   $161.8652   $161.87   $161.85   $161.90  
  7 purchase totals = $639.63       $695.8931   $695.89   $695.90   $695.90