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 $208.60   9.817%   $229.0783   $229.08   $229.10   $229.10  
  Purchase #2 $169.48   4.567%   $177.2202   $177.22   $177.20   $177.20  
  Purchase #3 $26.75   8.315%   $28.9743   $28.97   $28.95   $29.00  
  Purchase #4 $247.63   11.567%   $276.2734   $276.27   $276.25   $276.30  
  Purchase #5 $233.58   6.446%   $248.6366   $248.64   $248.65   $248.60  
  Purchase #6 $17.75   6.380%   $18.8825   $18.88   $18.90   $18.90  
  Purchase #7 $66.98   6.654%   $71.4368   $71.44   $71.45   $71.40  
  7 purchase totals = $970.77       $1,050.5021   $1,050.50   $1,050.50   $1,050.50