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 $79.50   9.132%   $86.7599   $86.76   $86.75   $86.80  
  Purchase #2 $116.25   6.368%   $123.6528   $123.65   $123.65   $123.70  
  Purchase #3 $68.84   10.287%   $75.9216   $75.92   $75.90   $75.90  
  Purchase #4 $238.32   12.654%   $268.477   $268.48   $268.50   $268.50  
  Purchase #5 $52.35   12.359%   $58.8199   $58.82   $58.80   $58.80  
  Purchase #6 $76.36   5.512%   $80.569   $80.57   $80.55   $80.60  
  Purchase #7 $60.92   10.268%   $67.1753   $67.18   $67.20   $67.20  
  7 purchase totals = $692.54       $761.3755   $761.38   $761.35   $761.50