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 $76.68   8.548%   $83.2346   $83.23   $83.25   $83.20  
  Purchase #2 $58.96   13.110%   $66.6897   $66.69   $66.70   $66.70  
  Purchase #3 $248.69   4.682%   $260.3337   $260.33   $260.35   $260.30  
  Purchase #4 $85.70   8.529%   $93.0094   $93.01   $93.00   $93.00  
  Purchase #5 $116.81   10.787%   $129.4103   $129.41   $129.40   $129.40  
  Purchase #6 $64.90   11.701%   $72.4939   $72.49   $72.50   $72.50  
  Purchase #7 $50.64   13.493%   $57.4729   $57.47   $57.45   $57.50  
  7 purchase totals = $702.38       $762.6445   $762.63   $762.65   $762.60