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 $232.98   6.320%   $247.7043   $247.70   $247.70   $247.70  
  Purchase #2 $247.76   12.161%   $277.8901   $277.89   $277.90   $277.90  
  Purchase #3 $153.90   12.709%   $173.4592   $173.46   $173.45   $173.50  
  Purchase #4 $175.59   13.622%   $199.5089   $199.51   $199.50   $199.50  
  Purchase #5 $229.97   7.543%   $247.3166   $247.32   $247.30   $247.30  
  Purchase #6 $124.60   6.391%   $132.5632   $132.56   $132.55   $132.60  
  Purchase #7 $179.86   11.803%   $201.0889   $201.09   $201.10   $201.10  
  7 purchase totals = $1,344.66       $1,479.5312   $1,479.53   $1,479.50   $1,479.60