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 $234.30   8.801%   $254.9207   $254.92   $254.90   $254.90  
  Purchase #2 $34.42   11.425%   $38.3525   $38.35   $38.35   $38.40  
  Purchase #3 $75.25   3.124%   $77.6008   $77.60   $77.60   $77.60  
  Purchase #4 $197.38   9.545%   $216.2199   $216.22   $216.20   $216.20  
  Purchase #5 $109.34   9.468%   $119.6923   $119.69   $119.70   $119.70  
  Purchase #6 $169.55   5.689%   $179.1957   $179.20   $179.20   $179.20  
  Purchase #7 $140.57   4.137%   $146.3854   $146.39   $146.40   $146.40  
  7 purchase totals = $960.81       $1,032.3673   $1,032.37   $1,032.35   $1,032.40