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 $243.29   11.394%   $271.0105   $271.01   $271.00   $271.00  
  Purchase #2 $145.44   7.391%   $156.1895   $156.19   $156.20   $156.20  
  Purchase #3 $103.46   3.835%   $107.4277   $107.43   $107.45   $107.40  
  Purchase #4 $92.26   4.659%   $96.5584   $96.56   $96.55   $96.60  
  Purchase #5 $196.25   9.176%   $214.2579   $214.26   $214.25   $214.30  
  Purchase #6 $175.45   7.570%   $188.7316   $188.73   $188.75   $188.70  
  Purchase #7 $177.64   9.222%   $194.022   $194.02   $194.00   $194.00  
  7 purchase totals = $1,133.79       $1,228.1976   $1,228.20   $1,228.20   $1,228.20