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 $214.57   11.589%   $239.4365   $239.44   $239.45   $239.40  
  Purchase #2 $185.61   6.302%   $197.3071   $197.31   $197.30   $197.30  
  Purchase #3 $81.83   7.688%   $88.1211   $88.12   $88.10   $88.10  
  Purchase #4 $20.98   7.287%   $22.5088   $22.51   $22.50   $22.50  
  Purchase #5 $60.75   4.529%   $63.5014   $63.50   $63.50   $63.50  
  Purchase #6 $211.62   4.143%   $220.3874   $220.39   $220.40   $220.40  
  Purchase #7 $169.79   9.139%   $185.3071   $185.31   $185.30   $185.30  
  7 purchase totals = $945.15       $1,016.5694   $1,016.58   $1,016.55   $1,016.50