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 $244.53   5.611%   $258.2506   $258.25   $258.25   $258.30  
  Purchase #2 $89.34   13.288%   $101.2115   $101.21   $101.20   $101.20  
  Purchase #3 $53.72   8.766%   $58.4291   $58.43   $58.45   $58.40  
  Purchase #4 $228.70   11.388%   $254.7444   $254.74   $254.75   $254.70  
  Purchase #5 $50.31   5.437%   $53.0454   $53.05   $53.05   $53.00  
  Purchase #6 $224.39   11.459%   $250.1029   $250.10   $250.10   $250.10  
  Purchase #7 $44.79   6.207%   $47.5701   $47.57   $47.55   $47.60  
  7 purchase totals = $935.78       $1,023.3540   $1,023.35   $1,023.35   $1,023.30