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 $32.54   9.833%   $35.7397   $35.74   $35.75   $35.70  
  Purchase #2 $227.48   5.487%   $239.9618   $239.96   $239.95   $240.00  
  Purchase #3 $176.28   5.701%   $186.3297   $186.33   $186.35   $186.30  
  Purchase #4 $9.80   11.334%   $10.9107   $10.91   $10.90   $10.90  
  Purchase #5 $157.25   9.765%   $172.6055   $172.61   $172.60   $172.60  
  Purchase #6 $247.27   10.686%   $273.6933   $273.69   $273.70   $273.70  
  Purchase #7 $103.53   12.505%   $116.4764   $116.48   $116.50   $116.50  
  7 purchase totals = $954.15       $1,035.7171   $1,035.72   $1,035.75   $1,035.70