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 $224.26   11.607%   $250.2899   $250.29   $250.30   $250.30  
  Purchase #2 $25.36   8.219%   $27.4443   $27.44   $27.45   $27.40  
  Purchase #3 $184.38   8.395%   $199.8587   $199.86   $199.85   $199.90  
  Purchase #4 $170.46   9.439%   $186.5497   $186.55   $186.55   $186.50  
  Purchase #5 $165.80   3.290%   $171.2548   $171.25   $171.25   $171.30  
  Purchase #6 $213.27   6.108%   $226.2965   $226.30   $226.30   $226.30  
  Purchase #7 $75.38   12.691%   $84.9465   $84.95   $84.95   $84.90  
  7 purchase totals = $1,058.91       $1,146.6404   $1,146.64   $1,146.65   $1,146.60