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 $192.74   4.464%   $201.3439   $201.34   $201.35   $201.30  
  Purchase #2 $14.28   11.581%   $15.9338   $15.93   $15.95   $15.90  
  Purchase #3 $136.32   4.597%   $142.5866   $142.59   $142.60   $142.60  
  Purchase #4 $205.80   4.300%   $214.6494   $214.65   $214.65   $214.60  
  Purchase #5 $79.43   10.333%   $87.6375   $87.64   $87.65   $87.60  
  Purchase #6 $226.92   13.487%   $257.5247   $257.52   $257.50   $257.50  
  Purchase #7 $69.94   9.643%   $76.6843   $76.68   $76.70   $76.70  
  7 purchase totals = $925.43       $996.3602   $996.35   $996.40   $996.20