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 $227.41   8.165%   $245.978   $245.98   $246.00   $246.00  
  Purchase #2 $69.83   7.826%   $75.2949   $75.29   $75.30   $75.30  
  Purchase #3 $129.39   7.188%   $138.6906   $138.69   $138.70   $138.70  
  Purchase #4 $134.93   7.387%   $144.8973   $144.90   $144.90   $144.90  
  Purchase #5 $145.81   9.153%   $159.156   $159.16   $159.15   $159.20  
  Purchase #6 $233.68   6.740%   $249.43   $249.43   $249.45   $249.40  
  Purchase #7 $134.77   8.349%   $146.0219   $146.02   $146.00   $146.00  
  7 purchase totals = $1,075.82       $1,159.4687   $1,159.47   $1,159.50   $1,159.50