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 $80.35   6.625%   $85.6732   $85.67   $85.65   $85.70  
  Purchase #2 $219.70   6.859%   $234.7692   $234.77   $234.75   $234.80  
  Purchase #3 $36.77   3.224%   $37.9555   $37.96   $37.95   $38.00  
  Purchase #4 $63.74   13.314%   $72.2263   $72.23   $72.25   $72.20  
  Purchase #5 $27.50   8.434%   $29.8194   $29.82   $29.80   $29.80  
  Purchase #6 $165.70   5.756%   $175.2377   $175.24   $175.25   $175.20  
  Purchase #7 $156.90   4.105%   $163.3407   $163.34   $163.35   $163.30  
  7 purchase totals = $750.66       $799.0220   $799.03   $799.00   $799.00