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 $224.61   13.264%   $254.4023   $254.40   $254.40   $254.40  
  Purchase #2 $98.29   13.427%   $111.4874   $111.49   $111.50   $111.50  
  Purchase #3 $136.66   12.751%   $154.0855   $154.09   $154.10   $154.10  
  Purchase #4 $188.57   13.811%   $214.6134   $214.61   $214.60   $214.60  
  Purchase #5 $119.52   4.527%   $124.9307   $124.93   $124.95   $124.90  
  Purchase #6 $88.69   4.816%   $92.9613   $92.96   $92.95   $93.00  
  Purchase #7 $125.72   8.208%   $136.0391   $136.04   $136.05   $136.00  
  7 purchase totals = $982.06       $1,088.5197   $1,088.52   $1,088.55   $1,088.50