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 $185.69   9.860%   $203.999   $204.00   $204.00   $204.00  
  Purchase #2 $82.61   10.169%   $91.0106   $91.01   $91.00   $91.00  
  Purchase #3 $182.29   8.638%   $198.0362   $198.04   $198.05   $198.00  
  Purchase #4 $139.73   5.529%   $147.4557   $147.46   $147.45   $147.50  
  Purchase #5 $194.89   5.838%   $206.2677   $206.27   $206.25   $206.30  
  Purchase #6 $169.80   8.726%   $184.6167   $184.62   $184.60   $184.60  
  Purchase #7 $8.98   10.155%   $9.8919   $9.89   $9.90   $9.90  
  7 purchase totals = $963.99       $1,041.2778   $1,041.29   $1,041.25   $1,041.30