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 $23.87   8.848%   $25.982   $25.98   $26.00   $26.00  
  Purchase #2 $64.69   5.851%   $68.475   $68.48   $68.50   $68.50  
  Purchase #3 $241.36   10.331%   $266.2949   $266.29   $266.30   $266.30  
  Purchase #4 $184.77   11.492%   $206.0038   $206.00   $206.00   $206.00  
  Purchase #5 $80.47   13.315%   $91.1846   $91.18   $91.20   $91.20  
  Purchase #6 $144.93   5.662%   $153.1359   $153.14   $153.15   $153.10  
  Purchase #7 $89.65   11.617%   $100.0646   $100.06   $100.05   $100.10  
  7 purchase totals = $829.74       $911.1408   $911.13   $911.20   $911.20