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 $233.96   5.292%   $246.3412   $246.34   $246.35   $246.30  
  Purchase #2 $41.43   8.388%   $44.9051   $44.91   $44.90   $44.90  
  Purchase #3 $179.72   4.284%   $187.4192   $187.42   $187.40   $187.40  
  Purchase #4 $166.64   10.512%   $184.1572   $184.16   $184.15   $184.20  
  Purchase #5 $239.70   3.376%   $247.7923   $247.79   $247.80   $247.80  
  Purchase #6 $49.30   9.799%   $54.1309   $54.13   $54.15   $54.10  
  Purchase #7 $230.63   12.820%   $260.1968   $260.20   $260.20   $260.20  
  7 purchase totals = $1,141.38       $1,224.9427   $1,224.95   $1,224.95   $1,224.90