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 $104.51   13.842%   $118.9763   $118.98   $119.00   $119.00  
  Purchase #2 $240.71   8.741%   $261.7505   $261.75   $261.75   $261.80  
  Purchase #3 $161.70   7.612%   $174.0086   $174.01   $174.00   $174.00  
  Purchase #4 $121.31   4.746%   $127.0674   $127.07   $127.05   $127.10  
  Purchase #5 $76.86   4.382%   $80.228   $80.23   $80.25   $80.20  
  Purchase #6 $191.94   5.309%   $202.1301   $202.13   $202.15   $202.10  
  Purchase #7 $164.77   11.286%   $183.3659   $183.37   $183.35   $183.40  
  7 purchase totals = $1,061.80       $1,147.5268   $1,147.54   $1,147.55   $1,147.60