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 $75.97   10.839%   $84.2044   $84.20   $84.20   $84.20  
  Purchase #2 $161.87   7.467%   $173.9568   $173.96   $173.95   $174.00  
  Purchase #3 $67.66   3.687%   $70.1546   $70.15   $70.15   $70.20  
  Purchase #4 $177.80   10.729%   $196.8762   $196.88   $196.90   $196.90  
  Purchase #5 $164.50   5.249%   $173.1346   $173.13   $173.15   $173.10  
  Purchase #6 $125.32   4.289%   $130.695   $130.70   $130.70   $130.70  
  Purchase #7 $133.52   8.226%   $144.5034   $144.50   $144.50   $144.50  
  7 purchase totals = $906.64       $973.5250   $973.52   $973.55   $973.60