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 $189.97   11.750%   $212.2915   $212.29   $212.30   $212.30  
  Purchase #2 $232.67   7.569%   $250.2808   $250.28   $250.30   $250.30  
  Purchase #3 $50.86   9.679%   $55.7827   $55.78   $55.80   $55.80  
  Purchase #4 $23.82   8.603%   $25.8692   $25.87   $25.85   $25.90  
  Purchase #5 $5.91   6.613%   $6.3008   $6.30   $6.30   $6.30  
  Purchase #6 $158.44   5.252%   $166.7613   $166.76   $166.75   $166.80  
  Purchase #7 $224.68   10.797%   $248.9387   $248.94   $248.95   $248.90  
  7 purchase totals = $886.35       $966.2250   $966.22   $966.25   $966.30