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 $66.48   8.688%   $72.2558   $72.26   $72.25   $72.30  
  Purchase #2 $90.51   4.222%   $94.3313   $94.33   $94.35   $94.30  
  Purchase #3 $39.99   6.824%   $42.7189   $42.72   $42.70   $42.70  
  Purchase #4 $218.30   6.179%   $231.7888   $231.79   $231.80   $231.80  
  Purchase #5 $186.62   5.767%   $197.3824   $197.38   $197.40   $197.40  
  Purchase #6 $188.45   5.707%   $199.2048   $199.20   $199.20   $199.20  
  Purchase #7 $176.82   13.538%   $200.7579   $200.76   $200.75   $200.80  
  7 purchase totals = $967.17       $1,038.4399   $1,038.44   $1,038.45   $1,038.50