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 $192.44   12.252%   $216.0177   $216.02   $216.00   $216.00  
  Purchase #2 $54.74   10.430%   $60.4494   $60.45   $60.45   $60.40  
  Purchase #3 $162.56   9.301%   $177.6797   $177.68   $177.70   $177.70  
  Purchase #4 $235.94   11.569%   $263.2359   $263.24   $263.25   $263.20  
  Purchase #5 $49.91   11.339%   $55.5693   $55.57   $55.55   $55.60  
  Purchase #6 $84.56   13.558%   $96.0246   $96.02   $96.00   $96.00  
  Purchase #7 $146.85   6.321%   $156.1324   $156.13   $156.15   $156.10  
  7 purchase totals = $927.00       $1,025.1090   $1,025.11   $1,025.10   $1,025.00