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 $204.91   9.297%   $223.9605   $223.96   $223.95   $224.00  
  Purchase #2 $26.74   10.197%   $29.4667   $29.47   $29.45   $29.50  
  Purchase #3 $242.29   8.171%   $262.0875   $262.09   $262.10   $262.10  
  Purchase #4 $240.32   11.318%   $267.5194   $267.52   $267.50   $267.50  
  Purchase #5 $197.83   5.378%   $208.4693   $208.47   $208.45   $208.50  
  Purchase #6 $85.72   9.659%   $93.9997   $94.00   $94.00   $94.00  
  Purchase #7 $155.79   3.654%   $161.4826   $161.48   $161.50   $161.50  
  7 purchase totals = $1,153.60       $1,246.9857   $1,246.99   $1,246.95   $1,247.10