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 $53.46   8.782%   $58.1549   $58.15   $58.15   $58.20  
  Purchase #2 $210.74   6.623%   $224.6973   $224.70   $224.70   $224.70  
  Purchase #3 $230.93   6.731%   $246.4739   $246.47   $246.45   $246.50  
  Purchase #4 $224.33   11.718%   $250.617   $250.62   $250.60   $250.60  
  Purchase #5 $103.90   12.736%   $117.1327   $117.13   $117.15   $117.10  
  Purchase #6 $78.56   8.535%   $85.2651   $85.27   $85.25   $85.30  
  Purchase #7 $176.28   8.196%   $190.7279   $190.73   $190.75   $190.70  
  7 purchase totals = $1,078.20       $1,173.0688   $1,173.07   $1,173.05   $1,173.10