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 $204.54   9.559%   $224.092   $224.09   $224.10   $224.10  
  Purchase #2 $217.53   11.631%   $242.8309   $242.83   $242.85   $242.80  
  Purchase #3 $168.41   9.543%   $184.4814   $184.48   $184.50   $184.50  
  Purchase #4 $228.94   13.715%   $260.3391   $260.34   $260.35   $260.30  
  Purchase #5 $240.60   4.792%   $252.1296   $252.13   $252.15   $252.10  
  Purchase #6 $5.36   11.343%   $5.968   $5.97   $5.95   $6.00  
  Purchase #7 $208.47   7.697%   $224.5159   $224.52   $224.50   $224.50  
  7 purchase totals = $1,273.85       $1,394.3569   $1,394.36   $1,394.40   $1,394.30