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 $214.38   7.744%   $230.9816   $230.98   $231.00   $231.00  
  Purchase #2 $224.93   8.847%   $244.8296   $244.83   $244.85   $244.80  
  Purchase #3 $36.75   9.506%   $40.2435   $40.24   $40.25   $40.20  
  Purchase #4 $186.57   3.735%   $193.5384   $193.54   $193.55   $193.50  
  Purchase #5 $23.37   12.631%   $26.3219   $26.32   $26.30   $26.30  
  Purchase #6 $33.31   4.644%   $34.8569   $34.86   $34.85   $34.90  
  Purchase #7 $175.95   11.168%   $195.6001   $195.60   $195.60   $195.60  
  7 purchase totals = $895.26       $966.3720   $966.37   $966.40   $966.30