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 $89.40   3.727%   $92.7319   $92.73   $92.75   $92.70  
  Purchase #2 $115.99   3.408%   $119.9429   $119.94   $119.95   $119.90  
  Purchase #3 $156.38   13.575%   $177.6086   $177.61   $177.60   $177.60  
  Purchase #4 $60.59   9.247%   $66.1928   $66.19   $66.20   $66.20  
  Purchase #5 $161.96   3.437%   $167.5266   $167.53   $167.55   $167.50  
  Purchase #6 $186.58   12.390%   $209.6973   $209.70   $209.70   $209.70  
  Purchase #7 $124.85   7.620%   $134.3636   $134.36   $134.35   $134.40  
  7 purchase totals = $895.75       $968.0637   $968.06   $968.10   $968.00