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 $66.63   12.180%   $74.7455   $74.75   $74.75   $74.70  
  Purchase #2 $244.84   4.135%   $254.9641   $254.96   $254.95   $255.00  
  Purchase #3 $154.33   7.311%   $165.6131   $165.61   $165.60   $165.60  
  Purchase #4 $166.65   4.572%   $174.2692   $174.27   $174.25   $174.30  
  Purchase #5 $215.74   9.670%   $236.6021   $236.60   $236.60   $236.60  
  Purchase #6 $115.81   10.679%   $128.1773   $128.18   $128.20   $128.20  
  Purchase #7 $249.95   13.578%   $283.8882   $283.89   $283.90   $283.90  
  7 purchase totals = $1,213.95       $1,318.2595   $1,318.26   $1,318.25   $1,318.30