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 $82.63   6.652%   $88.1265   $88.13   $88.15   $88.10  
  Purchase #2 $191.74   3.751%   $198.9322   $198.93   $198.95   $198.90  
  Purchase #3 $198.64   9.592%   $217.6935   $217.69   $217.70   $217.70  
  Purchase #4 $205.56   7.530%   $221.0387   $221.04   $221.05   $221.00  
  Purchase #5 $119.97   6.372%   $127.6145   $127.61   $127.60   $127.60  
  Purchase #6 $33.79   13.347%   $38.3   $38.30   $38.30   $38.30  
  Purchase #7 $29.83   12.399%   $33.5286   $33.53   $33.55   $33.50  
  7 purchase totals = $862.16       $925.2340   $925.23   $925.30   $925.10