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 $28.47   13.570%   $32.3334   $32.33   $32.35   $32.30  
  Purchase #2 $169.99   3.376%   $175.7289   $175.73   $175.75   $175.70  
  Purchase #3 $112.79   5.809%   $119.342   $119.34   $119.35   $119.30  
  Purchase #4 $161.43   3.511%   $167.0978   $167.10   $167.10   $167.10  
  Purchase #5 $14.65   11.153%   $16.2839   $16.28   $16.30   $16.30  
  Purchase #6 $242.84   9.474%   $265.8467   $265.85   $265.85   $265.80  
  Purchase #7 $182.47   7.191%   $195.5914   $195.59   $195.60   $195.60  
  7 purchase totals = $912.64       $972.2241   $972.22   $972.30   $972.10