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 $158.87   6.776%   $169.635   $169.64   $169.65   $169.60  
  Purchase #2 $45.64   9.353%   $49.9087   $49.91   $49.90   $49.90  
  Purchase #3 $128.27   4.281%   $133.7612   $133.76   $133.75   $133.80  
  Purchase #4 $14.40   13.743%   $16.379   $16.38   $16.40   $16.40  
  Purchase #5 $159.65   7.866%   $172.2081   $172.21   $172.20   $172.20  
  Purchase #6 $155.29   10.192%   $171.1172   $171.12   $171.10   $171.10  
  Purchase #7 $192.25   10.800%   $213.013   $213.01   $213.00   $213.00  
  7 purchase totals = $854.37       $926.0222   $926.03   $926.00   $926.00