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 $106.43   12.242%   $119.4592   $119.46   $119.45   $119.50  
  Purchase #2 $228.43   13.219%   $258.6262   $258.63   $258.65   $258.60  
  Purchase #3 $10.57   7.511%   $11.3639   $11.36   $11.35   $11.40  
  Purchase #4 $150.62   8.605%   $163.5809   $163.58   $163.60   $163.60  
  Purchase #5 $150.40   12.412%   $169.0676   $169.07   $169.05   $169.10  
  Purchase #6 $212.97   6.658%   $227.1495   $227.15   $227.15   $227.10  
  Purchase #7 $153.62   9.641%   $168.4305   $168.43   $168.45   $168.40  
  7 purchase totals = $1,013.04       $1,117.6778   $1,117.68   $1,117.70   $1,117.70