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 $41.70   8.393%   $45.1999   $45.20   $45.20   $45.20  
  Purchase #2 $195.55   6.194%   $207.6624   $207.66   $207.65   $207.70  
  Purchase #3 $113.27   8.484%   $122.8798   $122.88   $122.90   $122.90  
  Purchase #4 $247.28   5.510%   $260.9051   $260.91   $260.90   $260.90  
  Purchase #5 $220.29   4.649%   $230.5313   $230.53   $230.55   $230.50  
  Purchase #6 $126.74   8.375%   $137.3545   $137.35   $137.35   $137.40  
  Purchase #7 $15.51   8.773%   $16.8707   $16.87   $16.85   $16.90  
  7 purchase totals = $960.34       $1,021.4037   $1,021.40   $1,021.40   $1,021.50