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 $61.42   6.362%   $65.3275   $65.33   $65.35   $65.30  
  Purchase #2 $180.50   8.311%   $195.5014   $195.50   $195.50   $195.50  
  Purchase #3 $66.70   5.499%   $70.3678   $70.37   $70.35   $70.40  
  Purchase #4 $148.63   5.747%   $157.1718   $157.17   $157.15   $157.20  
  Purchase #5 $34.88   5.114%   $36.6638   $36.66   $36.65   $36.70  
  Purchase #6 $47.40   13.523%   $53.8099   $53.81   $53.80   $53.80  
  Purchase #7 $247.76   8.330%   $268.3984   $268.40   $268.40   $268.40  
  7 purchase totals = $787.29       $847.2406   $847.24   $847.20   $847.30