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 $140.88   5.762%   $148.9975   $149.00   $149.00   $149.00  
  Purchase #2 $91.75   3.619%   $95.0704   $95.07   $95.05   $95.10  
  Purchase #3 $214.36   3.111%   $221.0287   $221.03   $221.05   $221.00  
  Purchase #4 $180.72   13.200%   $204.575   $204.58   $204.60   $204.60  
  Purchase #5 $244.39   8.845%   $266.0063   $266.01   $266.00   $266.00  
  Purchase #6 $152.29   8.568%   $165.3382   $165.34   $165.35   $165.30  
  Purchase #7 $88.60   7.470%   $95.2184   $95.22   $95.20   $95.20  
  7 purchase totals = $1,112.99       $1,196.2345   $1,196.25   $1,196.25   $1,196.20