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 $61.46   12.843%   $69.3533   $69.35   $69.35   $69.40  
  Purchase #2 $193.34   6.432%   $205.7756   $205.78   $205.80   $205.80  
  Purchase #3 $138.71   9.389%   $151.7335   $151.73   $151.75   $151.70  
  Purchase #4 $147.30   13.539%   $167.2429   $167.24   $167.25   $167.20  
  Purchase #5 $247.39   12.124%   $277.3836   $277.38   $277.40   $277.40  
  Purchase #6 $20.93   12.589%   $23.5649   $23.56   $23.55   $23.60  
  Purchase #7 $95.34   5.868%   $100.9346   $100.93   $100.95   $100.90  
  7 purchase totals = $904.47       $995.9884   $995.97   $996.05   $996.00