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 $91.33   5.107%   $95.9942   $95.99   $96.00   $96.00  
  Purchase #2 $31.85   9.149%   $34.764   $34.76   $34.75   $34.80  
  Purchase #3 $248.93   10.144%   $274.1815   $274.18   $274.20   $274.20  
  Purchase #4 $142.88   12.472%   $160.7   $160.70   $160.70   $160.70  
  Purchase #5 $242.46   12.618%   $273.0536   $273.05   $273.05   $273.10  
  Purchase #6 $219.43   3.405%   $226.9016   $226.90   $226.90   $226.90  
  Purchase #7 $36.78   9.237%   $40.1774   $40.18   $40.20   $40.20  
  7 purchase totals = $1,013.66       $1,105.7723   $1,105.76   $1,105.80   $1,105.90