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 $33.99   6.321%   $36.1385   $36.14   $36.15   $36.10  
  Purchase #2 $183.92   8.492%   $199.5385   $199.54   $199.55   $199.50  
  Purchase #3 $209.93   4.828%   $220.0654   $220.07   $220.05   $220.10  
  Purchase #4 $8.86   5.661%   $9.3616   $9.36   $9.35   $9.40  
  Purchase #5 $179.54   12.294%   $201.6126   $201.61   $201.60   $201.60  
  Purchase #6 $205.29   8.831%   $223.4192   $223.42   $223.40   $223.40  
  Purchase #7 $212.57   6.641%   $226.6868   $226.69   $226.70   $226.70  
  7 purchase totals = $1,034.10       $1,116.8226   $1,116.83   $1,116.80   $1,116.80