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 $196.50   12.243%   $220.5575   $220.56   $220.55   $220.60  
  Purchase #2 $29.83   10.135%   $32.8533   $32.85   $32.85   $32.90  
  Purchase #3 $156.99   13.356%   $177.9576   $177.96   $177.95   $178.00  
  Purchase #4 $78.69   5.604%   $83.0998   $83.10   $83.10   $83.10  
  Purchase #5 $245.62   7.564%   $264.1987   $264.20   $264.20   $264.20  
  Purchase #6 $165.89   3.270%   $171.3146   $171.31   $171.30   $171.30  
  Purchase #7 $192.48   11.675%   $214.952   $214.95   $214.95   $215.00  
  7 purchase totals = $1,066.00       $1,164.9335   $1,164.93   $1,164.90   $1,165.10