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 $33.42   4.580%   $34.9506   $34.95   $34.95   $35.00  
  Purchase #2 $183.35   10.610%   $202.8034   $202.80   $202.80   $202.80  
  Purchase #3 $143.77   4.476%   $150.2051   $150.21   $150.20   $150.20  
  Purchase #4 $106.38   9.291%   $116.2638   $116.26   $116.25   $116.30  
  Purchase #5 $28.30   9.160%   $30.8923   $30.89   $30.90   $30.90  
  Purchase #6 $204.88   3.449%   $211.9463   $211.95   $211.95   $211.90  
  Purchase #7 $214.27   5.415%   $225.8727   $225.87   $225.85   $225.90  
  7 purchase totals = $914.37       $972.9342   $972.93   $972.90   $973.00