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 $68.47   10.542%   $75.6881   $75.69   $75.70   $75.70  
  Purchase #2 $173.85   13.256%   $196.8956   $196.90   $196.90   $196.90  
  Purchase #3 $87.45   13.406%   $99.1735   $99.17   $99.15   $99.20  
  Purchase #4 $241.65   4.103%   $251.5649   $251.56   $251.55   $251.60  
  Purchase #5 $128.67   12.591%   $144.8708   $144.87   $144.85   $144.90  
  Purchase #6 $191.85   7.595%   $206.421   $206.42   $206.40   $206.40  
  Purchase #7 $135.36   6.438%   $144.0745   $144.07   $144.05   $144.10  
  7 purchase totals = $1,027.30       $1,118.6884   $1,118.68   $1,118.60   $1,118.80