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 $214.59   13.717%   $244.0253   $244.03   $244.05   $244.00  
  Purchase #2 $43.77   3.510%   $45.3063   $45.31   $45.30   $45.30  
  Purchase #3 $159.65   5.599%   $168.5888   $168.59   $168.60   $168.60  
  Purchase #4 $16.49   7.337%   $17.6999   $17.70   $17.70   $17.70  
  Purchase #5 $55.33   4.828%   $58.0013   $58.00   $58.00   $58.00  
  Purchase #6 $223.93   12.492%   $251.9033   $251.90   $251.90   $251.90  
  Purchase #7 $128.64   9.698%   $141.1155   $141.12   $141.10   $141.10  
  7 purchase totals = $842.40       $926.6404   $926.65   $926.65   $926.60