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 $97.45   12.320%   $109.4558   $109.46   $109.45   $109.50  
  Purchase #2 $128.73   5.775%   $136.1642   $136.16   $136.15   $136.20  
  Purchase #3 $36.57   3.524%   $37.8587   $37.86   $37.85   $37.90  
  Purchase #4 $134.27   11.770%   $150.0736   $150.07   $150.05   $150.10  
  Purchase #5 $150.69   4.441%   $157.3821   $157.38   $157.40   $157.40  
  Purchase #6 $32.70   10.394%   $36.0988   $36.10   $36.10   $36.10  
  Purchase #7 $154.30   4.102%   $160.6294   $160.63   $160.65   $160.60  
  7 purchase totals = $734.71       $787.6626   $787.66   $787.65   $787.80