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 $23.41   12.580%   $26.355   $26.36   $26.35   $26.40  
  Purchase #2 $108.31   9.746%   $118.8659   $118.87   $118.85   $118.90  
  Purchase #3 $198.42   13.389%   $224.9865   $224.99   $225.00   $225.00  
  Purchase #4 $199.57   9.362%   $218.2537   $218.25   $218.25   $218.30  
  Purchase #5 $59.43   12.658%   $66.9526   $66.95   $66.95   $67.00  
  Purchase #6 $135.46   5.449%   $142.8412   $142.84   $142.85   $142.80  
  Purchase #7 $158.44   3.644%   $164.2136   $164.21   $164.20   $164.20  
  7 purchase totals = $883.04       $962.4685   $962.47   $962.45   $962.60