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 $113.27   9.759%   $124.324   $124.32   $124.30   $124.30  
  Purchase #2 $22.52   8.183%   $24.3628   $24.36   $24.35   $24.40  
  Purchase #3 $219.73   12.727%   $247.695   $247.70   $247.70   $247.70  
  Purchase #4 $250.31   6.627%   $266.898   $266.90   $266.90   $266.90  
  Purchase #5 $31.29   3.186%   $32.2869   $32.29   $32.30   $32.30  
  Purchase #6 $150.69   5.476%   $158.9418   $158.94   $158.95   $158.90  
  Purchase #7 $156.52   9.824%   $171.8965   $171.90   $171.90   $171.90  
  7 purchase totals = $944.33       $1,026.4050   $1,026.41   $1,026.40   $1,026.40