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 $111.36   13.678%   $126.5918   $126.59   $126.60   $126.60  
  Purchase #2 $230.98   12.411%   $259.6469   $259.65   $259.65   $259.60  
  Purchase #3 $26.27   10.779%   $29.1016   $29.10   $29.10   $29.10  
  Purchase #4 $237.68   12.600%   $267.6277   $267.63   $267.65   $267.60  
  Purchase #5 $202.95   6.326%   $215.7886   $215.79   $215.80   $215.80  
  Purchase #6 $101.34   7.563%   $109.0043   $109.00   $109.00   $109.00  
  Purchase #7 $35.51   5.519%   $37.4698   $37.47   $37.45   $37.50  
  7 purchase totals = $946.09       $1,045.2307   $1,045.23   $1,045.25   $1,045.20