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 $37.63   10.128%   $41.4412   $41.44   $41.45   $41.40  
  Purchase #2 $94.38   7.448%   $101.4094   $101.41   $101.40   $101.40  
  Purchase #3 $226.47   8.718%   $246.2137   $246.21   $246.20   $246.20  
  Purchase #4 $157.87   10.548%   $174.5221   $174.52   $174.50   $174.50  
  Purchase #5 $70.73   7.570%   $76.0843   $76.08   $76.10   $76.10  
  Purchase #6 $208.97   3.521%   $216.3278   $216.33   $216.35   $216.30  
  Purchase #7 $150.27   7.790%   $161.976   $161.98   $162.00   $162.00  
  7 purchase totals = $946.32       $1,017.9745   $1,017.97   $1,018.00   $1,017.90