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 $177.44   13.746%   $201.8309   $201.83   $201.85   $201.80  
  Purchase #2 $209.79   8.678%   $227.9956   $228.00   $228.00   $228.00  
  Purchase #3 $219.77   13.273%   $248.9401   $248.94   $248.95   $248.90  
  Purchase #4 $81.26   3.112%   $83.7888   $83.79   $83.80   $83.80  
  Purchase #5 $182.26   8.187%   $197.1816   $197.18   $197.20   $197.20  
  Purchase #6 $29.80   13.667%   $33.8728   $33.87   $33.85   $33.90  
  Purchase #7 $68.63   11.607%   $76.5959   $76.60   $76.60   $76.60  
  7 purchase totals = $968.95       $1,070.2057   $1,070.21   $1,070.25   $1,070.20