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 $230.42   13.747%   $262.0958   $262.10   $262.10   $262.10  
  Purchase #2 $13.44   8.120%   $14.5313   $14.53   $14.55   $14.50  
  Purchase #3 $96.57   8.505%   $104.7833   $104.78   $104.80   $104.80  
  Purchase #4 $52.54   10.316%   $57.96   $57.96   $57.95   $58.00  
  Purchase #5 $249.43   8.841%   $271.4821   $271.48   $271.50   $271.50  
  Purchase #6 $60.30   7.434%   $64.7827   $64.78   $64.80   $64.80  
  Purchase #7 $240.89   4.322%   $251.3013   $251.30   $251.30   $251.30  
  7 purchase totals = $943.59       $1,026.9365   $1,026.93   $1,027.00   $1,027.00