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 $62.58   3.421%   $64.7209   $64.72   $64.70   $64.70  
  Purchase #2 $103.45   12.259%   $116.1319   $116.13   $116.15   $116.10  
  Purchase #3 $58.49   8.239%   $63.309   $63.31   $63.30   $63.30  
  Purchase #4 $217.96   3.459%   $225.4992   $225.50   $225.50   $225.50  
  Purchase #5 $9.83   7.137%   $10.5316   $10.53   $10.55   $10.50  
  Purchase #6 $179.74   8.482%   $194.9855   $194.99   $195.00   $195.00  
  Purchase #7 $239.68   12.387%   $269.3692   $269.37   $269.35   $269.40  
  7 purchase totals = $871.73       $944.5473   $944.55   $944.55   $944.50