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 $206.63   12.519%   $232.498   $232.50   $232.50   $232.50  
  Purchase #2 $84.40   9.700%   $92.5868   $92.59   $92.60   $92.60  
  Purchase #3 $201.62   9.201%   $220.1711   $220.17   $220.15   $220.20  
  Purchase #4 $51.26   6.236%   $54.4566   $54.46   $54.45   $54.50  
  Purchase #5 $105.70   3.596%   $109.501   $109.50   $109.50   $109.50  
  Purchase #6 $177.71   4.173%   $185.1258   $185.13   $185.15   $185.10  
  Purchase #7 $106.76   6.584%   $113.7891   $113.79   $113.80   $113.80  
  7 purchase totals = $934.08       $1,008.1284   $1,008.14   $1,008.15   $1,008.20