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 $59.93   12.127%   $67.1977   $67.20   $67.20   $67.20  
  Purchase #2 $71.89   6.207%   $76.3522   $76.35   $76.35   $76.40  
  Purchase #3 $152.87   9.848%   $167.9246   $167.92   $167.90   $167.90  
  Purchase #4 $126.43   6.147%   $134.2017   $134.20   $134.20   $134.20  
  Purchase #5 $230.78   12.191%   $258.9144   $258.91   $258.90   $258.90  
  Purchase #6 $229.85   10.174%   $253.2349   $253.23   $253.25   $253.20  
  Purchase #7 $137.88   12.504%   $155.1205   $155.12   $155.10   $155.10  
  7 purchase totals = $1,009.63       $1,112.9460   $1,112.93   $1,112.90   $1,112.90