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 $61.82   13.661%   $70.2652   $70.27   $70.25   $70.30  
  Purchase #2 $231.90   13.403%   $262.9816   $262.98   $263.00   $263.00  
  Purchase #3 $157.47   8.519%   $170.8849   $170.88   $170.90   $170.90  
  Purchase #4 $162.74   4.608%   $170.2391   $170.24   $170.25   $170.20  
  Purchase #5 $245.86   8.665%   $267.1638   $267.16   $267.15   $267.20  
  Purchase #6 $169.98   9.410%   $185.9751   $185.98   $186.00   $186.00  
  Purchase #7 $145.25   3.520%   $150.3628   $150.36   $150.35   $150.40  
  7 purchase totals = $1,175.02       $1,277.8725   $1,277.87   $1,277.90   $1,278.00