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 $235.33   11.526%   $262.4541   $262.45   $262.45   $262.50  
  Purchase #2 $232.33   12.286%   $260.8741   $260.87   $260.85   $260.90  
  Purchase #3 $228.26   9.498%   $249.9401   $249.94   $249.95   $249.90  
  Purchase #4 $73.49   3.418%   $76.0019   $76.00   $76.00   $76.00  
  Purchase #5 $244.40   5.451%   $257.7222   $257.72   $257.70   $257.70  
  Purchase #6 $61.66   6.707%   $65.7955   $65.80   $65.80   $65.80  
  Purchase #7 $48.54   10.349%   $53.5634   $53.56   $53.55   $53.60  
  7 purchase totals = $1,124.01       $1,226.3513   $1,226.34   $1,226.30   $1,226.40