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 $211.47   9.576%   $231.7204   $231.72   $231.70   $231.70  
  Purchase #2 $229.34   11.804%   $256.4113   $256.41   $256.40   $256.40  
  Purchase #3 $68.67   9.116%   $74.93   $74.93   $74.95   $74.90  
  Purchase #4 $156.26   6.389%   $166.2435   $166.24   $166.25   $166.20  
  Purchase #5 $143.71   9.735%   $157.7002   $157.70   $157.70   $157.70  
  Purchase #6 $49.32   9.420%   $53.9659   $53.97   $53.95   $54.00  
  Purchase #7 $205.25   5.157%   $215.8347   $215.83   $215.85   $215.80  
  7 purchase totals = $1,064.02       $1,156.8060   $1,156.80   $1,156.80   $1,156.70