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 $69.84   11.577%   $77.9254   $77.93   $77.95   $77.90  
  Purchase #2 $207.87   4.315%   $216.8396   $216.84   $216.85   $216.80  
  Purchase #3 $91.78   13.150%   $103.8491   $103.85   $103.85   $103.80  
  Purchase #4 $198.43   4.395%   $207.151   $207.15   $207.15   $207.20  
  Purchase #5 $40.26   8.624%   $43.732   $43.73   $43.75   $43.70  
  Purchase #6 $176.74   5.525%   $186.5049   $186.50   $186.50   $186.50  
  Purchase #7 $167.81   7.860%   $180.9999   $181.00   $181.00   $181.00  
  7 purchase totals = $952.73       $1,017.0019   $1,017.00   $1,017.05   $1,016.90