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 $215.69   12.102%   $241.7928   $241.79   $241.80   $241.80  
  Purchase #2 $62.98   13.251%   $71.3255   $71.33   $71.35   $71.30  
  Purchase #3 $201.48   12.834%   $227.3379   $227.34   $227.35   $227.30  
  Purchase #4 $183.68   3.529%   $190.1621   $190.16   $190.15   $190.20  
  Purchase #5 $228.25   9.138%   $249.1075   $249.11   $249.10   $249.10  
  Purchase #6 $92.49   10.288%   $102.0054   $102.01   $102.00   $102.00  
  Purchase #7 $75.70   7.496%   $81.3745   $81.37   $81.35   $81.40  
  7 purchase totals = $1,060.27       $1,163.1057   $1,163.11   $1,163.10   $1,163.10