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 $204.83   10.740%   $226.8287   $226.83   $226.85   $226.80  
  Purchase #2 $230.92   9.173%   $252.1023   $252.10   $252.10   $252.10  
  Purchase #3 $15.25   11.499%   $17.0036   $17.00   $17.00   $17.00  
  Purchase #4 $236.44   10.224%   $260.6136   $260.61   $260.60   $260.60  
  Purchase #5 $220.43   4.685%   $230.7571   $230.76   $230.75   $230.80  
  Purchase #6 $137.30   3.319%   $141.857   $141.86   $141.85   $141.90  
  Purchase #7 $114.36   13.780%   $130.1188   $130.12   $130.10   $130.10  
  7 purchase totals = $1,159.53       $1,259.2811   $1,259.28   $1,259.25   $1,259.30