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 $209.95   12.869%   $236.9685   $236.97   $236.95   $237.00  
  Purchase #2 $125.57   6.533%   $133.7735   $133.77   $133.75   $133.80  
  Purchase #3 $214.89   8.332%   $232.7946   $232.79   $232.80   $232.80  
  Purchase #4 $198.54   5.386%   $209.2334   $209.23   $209.25   $209.20  
  Purchase #5 $163.79   9.489%   $179.332   $179.33   $179.35   $179.30  
  Purchase #6 $33.85   5.103%   $35.5774   $35.58   $35.60   $35.60  
  Purchase #7 $7.66   5.247%   $8.0619   $8.06   $8.05   $8.10  
  7 purchase totals = $954.25       $1,035.7413   $1,035.73   $1,035.75   $1,035.80