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 $62.47   13.596%   $70.9634   $70.96   $70.95   $71.00  
  Purchase #2 $58.57   9.138%   $63.9221   $63.92   $63.90   $63.90  
  Purchase #3 $205.59   9.649%   $225.4274   $225.43   $225.45   $225.40  
  Purchase #4 $65.67   11.386%   $73.1472   $73.15   $73.15   $73.10  
  Purchase #5 $17.95   9.610%   $19.675   $19.68   $19.70   $19.70  
  Purchase #6 $53.25   4.281%   $55.5296   $55.53   $55.55   $55.50  
  Purchase #7 $249.33   5.446%   $262.9085   $262.91   $262.90   $262.90  
  7 purchase totals = $712.83       $771.5732   $771.58   $771.60   $771.50