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 $20.39   7.747%   $21.9696   $21.97   $21.95   $22.00  
  Purchase #2 $111.80   3.219%   $115.3988   $115.40   $115.40   $115.40  
  Purchase #3 $241.34   10.817%   $267.4457   $267.45   $267.45   $267.40  
  Purchase #4 $81.79   9.342%   $89.4308   $89.43   $89.45   $89.40  
  Purchase #5 $142.65   3.835%   $148.1206   $148.12   $148.10   $148.10  
  Purchase #6 $129.84   11.265%   $144.4665   $144.47   $144.45   $144.50  
  Purchase #7 $197.39   6.812%   $210.8362   $210.84   $210.85   $210.80  
  7 purchase totals = $925.20       $997.6682   $997.68   $997.65   $997.60