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 $183.93   11.400%   $204.898   $204.90   $204.90   $204.90  
  Purchase #2 $47.67   12.794%   $53.7689   $53.77   $53.75   $53.80  
  Purchase #3 $51.92   4.855%   $54.4407   $54.44   $54.45   $54.40  
  Purchase #4 $129.87   6.668%   $138.5297   $138.53   $138.55   $138.50  
  Purchase #5 $162.67   6.853%   $173.8178   $173.82   $173.80   $173.80  
  Purchase #6 $247.68   6.185%   $262.999   $263.00   $263.00   $263.00  
  Purchase #7 $84.60   13.849%   $96.3163   $96.32   $96.30   $96.30  
  7 purchase totals = $908.34       $984.7704   $984.78   $984.75   $984.70