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 $225.39   13.449%   $255.7027   $255.70   $255.70   $255.70  
  Purchase #2 $39.53   5.348%   $41.6441   $41.64   $41.65   $41.60  
  Purchase #3 $219.71   9.276%   $240.0903   $240.09   $240.10   $240.10  
  Purchase #4 $153.65   6.296%   $163.3238   $163.32   $163.30   $163.30  
  Purchase #5 $86.74   8.114%   $93.7781   $93.78   $93.80   $93.80  
  Purchase #6 $204.44   3.293%   $211.1722   $211.17   $211.15   $211.20  
  Purchase #7 $54.50   8.414%   $59.0856   $59.09   $59.10   $59.10  
  7 purchase totals = $983.96       $1,064.7968   $1,064.79   $1,064.80   $1,064.80