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 $233.64   8.353%   $253.1559   $253.16   $253.15   $253.20  
  Purchase #2 $213.36   11.419%   $237.7236   $237.72   $237.70   $237.70  
  Purchase #3 $104.82   3.703%   $108.7015   $108.70   $108.70   $108.70  
  Purchase #4 $167.55   10.861%   $185.7476   $185.75   $185.75   $185.70  
  Purchase #5 $116.83   8.770%   $127.076   $127.08   $127.10   $127.10  
  Purchase #6 $104.86   5.321%   $110.4396   $110.44   $110.45   $110.40  
  Purchase #7 $175.52   3.686%   $181.9897   $181.99   $182.00   $182.00  
  7 purchase totals = $1,116.58       $1,204.8339   $1,204.84   $1,204.85   $1,204.80