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 $153.53   8.256%   $166.2054   $166.21   $166.20   $166.20  
  Purchase #2 $196.94   11.308%   $219.21   $219.21   $219.20   $219.20  
  Purchase #3 $193.81   7.291%   $207.9407   $207.94   $207.95   $207.90  
  Purchase #4 $239.93   12.337%   $269.5302   $269.53   $269.55   $269.50  
  Purchase #5 $186.29   5.211%   $195.9976   $196.00   $196.00   $196.00  
  Purchase #6 $96.48   6.683%   $102.9278   $102.93   $102.95   $102.90  
  Purchase #7 $199.74   12.569%   $224.8453   $224.85   $224.85   $224.80  
  7 purchase totals = $1,266.72       $1,386.6570   $1,386.67   $1,386.70   $1,386.50