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 $177.67   9.761%   $195.0124   $195.01   $195.00   $195.00  
  Purchase #2 $157.77   11.219%   $175.4702   $175.47   $175.45   $175.50  
  Purchase #3 $107.82   7.428%   $115.8289   $115.83   $115.85   $115.80  
  Purchase #4 $198.70   9.868%   $218.3077   $218.31   $218.30   $218.30  
  Purchase #5 $89.58   10.499%   $98.985   $98.99   $99.00   $99.00  
  Purchase #6 $81.92   11.454%   $91.3031   $91.30   $91.30   $91.30  
  Purchase #7 $116.51   12.262%   $130.7965   $130.80   $130.80   $130.80  
  7 purchase totals = $929.97       $1,025.7038   $1,025.71   $1,025.70   $1,025.70