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 $60.50   12.353%   $67.9736   $67.97   $67.95   $68.00  
  Purchase #2 $126.95   5.509%   $133.9437   $133.94   $133.95   $133.90  
  Purchase #3 $181.87   5.588%   $192.0329   $192.03   $192.05   $192.00  
  Purchase #4 $236.55   3.387%   $244.5619   $244.56   $244.55   $244.60  
  Purchase #5 $180.31   3.272%   $186.2097   $186.21   $186.20   $186.20  
  Purchase #6 $246.94   4.608%   $258.319   $258.32   $258.30   $258.30  
  Purchase #7 $212.73   9.749%   $233.469   $233.47   $233.45   $233.50  
  7 purchase totals = $1,245.85       $1,316.5098   $1,316.50   $1,316.45   $1,316.50