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 $50.42   6.237%   $53.5647   $53.56   $53.55   $53.60  
  Purchase #2 $189.83   3.405%   $196.2937   $196.29   $196.30   $196.30  
  Purchase #3 $80.90   4.465%   $84.5122   $84.51   $84.50   $84.50  
  Purchase #4 $67.65   9.674%   $74.1945   $74.19   $74.20   $74.20  
  Purchase #5 $124.65   7.286%   $133.732   $133.73   $133.75   $133.70  
  Purchase #6 $7.80   11.707%   $8.7131   $8.71   $8.70   $8.70  
  Purchase #7 $205.43   9.442%   $224.8267   $224.83   $224.85   $224.80  
  7 purchase totals = $726.68       $775.8369   $775.82   $775.85   $775.80