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 $156.74   11.693%   $175.0676   $175.07   $175.05   $175.10  
  Purchase #2 $213.58   12.507%   $240.2925   $240.29   $240.30   $240.30  
  Purchase #3 $33.92   6.867%   $36.2493   $36.25   $36.25   $36.20  
  Purchase #4 $241.63   11.150%   $268.5717   $268.57   $268.55   $268.60  
  Purchase #5 $41.83   11.409%   $46.6024   $46.60   $46.60   $46.60  
  Purchase #6 $122.64   7.801%   $132.2071   $132.21   $132.20   $132.20  
  Purchase #7 $173.97   12.874%   $196.3669   $196.37   $196.35   $196.40  
  7 purchase totals = $984.31       $1,095.3575   $1,095.36   $1,095.30   $1,095.40