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 $125.32   12.226%   $140.6416   $140.64   $140.65   $140.60  
  Purchase #2 $169.84   4.373%   $177.2671   $177.27   $177.25   $177.30  
  Purchase #3 $41.96   5.805%   $44.3958   $44.40   $44.40   $44.40  
  Purchase #4 $228.97   11.163%   $254.5299   $254.53   $254.55   $254.50  
  Purchase #5 $95.27   11.314%   $106.0488   $106.05   $106.05   $106.00  
  Purchase #6 $171.51   12.231%   $192.4874   $192.49   $192.50   $192.50  
  Purchase #7 $179.44   9.269%   $196.0723   $196.07   $196.05   $196.10  
  7 purchase totals = $1,012.31       $1,111.4429   $1,111.45   $1,111.45   $1,111.40