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 $92.34   5.218%   $97.1583   $97.16   $97.15   $97.20  
  Purchase #2 $161.49   9.137%   $176.2453   $176.25   $176.25   $176.20  
  Purchase #3 $166.83   11.840%   $186.5827   $186.58   $186.60   $186.60  
  Purchase #4 $199.88   6.680%   $213.232   $213.23   $213.25   $213.20  
  Purchase #5 $127.51   5.237%   $134.1877   $134.19   $134.20   $134.20  
  Purchase #6 $159.55   13.463%   $181.0302   $181.03   $181.05   $181.00  
  Purchase #7 $205.81   12.199%   $230.9168   $230.92   $230.90   $230.90  
  7 purchase totals = $1,113.41       $1,219.3530   $1,219.36   $1,219.40   $1,219.30