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 $5.68   13.214%   $6.4306   $6.43   $6.45   $6.40  
  Purchase #2 $237.99   11.454%   $265.2494   $265.25   $265.25   $265.20  
  Purchase #3 $77.60   8.440%   $84.1494   $84.15   $84.15   $84.10  
  Purchase #4 $218.97   6.212%   $232.5724   $232.57   $232.55   $232.60  
  Purchase #5 $90.97   12.154%   $102.0265   $102.03   $102.05   $102.00  
  Purchase #6 $64.55   11.310%   $71.8506   $71.85   $71.85   $71.90  
  Purchase #7 $158.75   3.313%   $164.0094   $164.01   $164.00   $164.00  
  7 purchase totals = $854.51       $926.2883   $926.29   $926.30   $926.20