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 $179.49   12.592%   $202.0914   $202.09   $202.10   $202.10  
  Purchase #2 $240.68   7.376%   $258.4326   $258.43   $258.45   $258.40  
  Purchase #3 $244.46   6.366%   $260.0223   $260.02   $260.00   $260.00  
  Purchase #4 $61.39   8.368%   $66.5271   $66.53   $66.55   $66.50  
  Purchase #5 $91.93   3.372%   $95.0299   $95.03   $95.05   $95.00  
  Purchase #6 $112.48   10.626%   $124.4321   $124.43   $124.45   $124.40  
  Purchase #7 $41.96   10.284%   $46.2752   $46.28   $46.30   $46.30  
  7 purchase totals = $972.39       $1,052.8106   $1,052.81   $1,052.90   $1,052.70