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 $218.52   6.579%   $232.8964   $232.90   $232.90   $232.90  
  Purchase #2 $94.99   13.525%   $107.8374   $107.84   $107.85   $107.80  
  Purchase #3 $153.79   13.502%   $174.5547   $174.55   $174.55   $174.60  
  Purchase #4 $234.91   11.364%   $261.6052   $261.61   $261.60   $261.60  
  Purchase #5 $97.91   11.313%   $108.9866   $108.99   $109.00   $109.00  
  Purchase #6 $205.76   10.518%   $227.4018   $227.40   $227.40   $227.40  
  Purchase #7 $25.71   4.163%   $26.7803   $26.78   $26.80   $26.80  
  7 purchase totals = $1,031.59       $1,140.0624   $1,140.07   $1,140.10   $1,140.10