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 $250.49   11.513%   $279.3289   $279.33   $279.35   $279.30  
  Purchase #2 $39.80   10.574%   $44.0085   $44.01   $44.00   $44.00  
  Purchase #3 $36.56   11.309%   $40.6946   $40.69   $40.70   $40.70  
  Purchase #4 $48.45   10.439%   $53.5077   $53.51   $53.50   $53.50  
  Purchase #5 $227.80   7.682%   $245.2996   $245.30   $245.30   $245.30  
  Purchase #6 $202.92   11.221%   $225.6897   $225.69   $225.70   $225.70  
  Purchase #7 $165.64   3.346%   $171.1823   $171.18   $171.20   $171.20  
  7 purchase totals = $971.66       $1,059.7113   $1,059.71   $1,059.75   $1,059.70