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 $163.32   6.486%   $173.9129   $173.91   $173.90   $173.90  
  Purchase #2 $231.31   12.605%   $260.4666   $260.47   $260.45   $260.50  
  Purchase #3 $50.68   4.501%   $52.9611   $52.96   $52.95   $53.00  
  Purchase #4 $74.60   11.244%   $82.988   $82.99   $83.00   $83.00  
  Purchase #5 $176.30   8.845%   $191.8937   $191.89   $191.90   $191.90  
  Purchase #6 $57.96   12.338%   $65.1111   $65.11   $65.10   $65.10  
  Purchase #7 $214.87   8.601%   $233.351   $233.35   $233.35   $233.40  
  7 purchase totals = $969.04       $1,060.6844   $1,060.68   $1,060.65   $1,060.80