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 $68.36   10.862%   $75.7853   $75.79   $75.80   $75.80  
  Purchase #2 $220.90   10.123%   $243.2617   $243.26   $243.25   $243.30  
  Purchase #3 $116.35   9.652%   $127.5801   $127.58   $127.60   $127.60  
  Purchase #4 $169.64   5.336%   $178.692   $178.69   $178.70   $178.70  
  Purchase #5 $174.58   6.752%   $186.3676   $186.37   $186.35   $186.40  
  Purchase #6 $207.60   3.137%   $214.1124   $214.11   $214.10   $214.10  
  Purchase #7 $213.27   3.465%   $220.6598   $220.66   $220.65   $220.70  
  7 purchase totals = $1,170.70       $1,246.4589   $1,246.46   $1,246.45   $1,246.60