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 $224.68   12.753%   $253.3334   $253.33   $253.35   $253.30  
  Purchase #2 $199.64   8.332%   $216.274   $216.27   $216.25   $216.30  
  Purchase #3 $216.38   10.694%   $239.5197   $239.52   $239.50   $239.50  
  Purchase #4 $44.75   5.531%   $47.2251   $47.23   $47.25   $47.20  
  Purchase #5 $151.34   10.339%   $166.987   $166.99   $167.00   $167.00  
  Purchase #6 $216.71   8.444%   $235.009   $235.01   $235.00   $235.00  
  Purchase #7 $33.39   3.805%   $34.6605   $34.66   $34.65   $34.70  
  7 purchase totals = $1,086.89       $1,193.0087   $1,193.01   $1,193.00   $1,193.00