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 $220.92   11.258%   $245.7912   $245.79   $245.80   $245.80  
  Purchase #2 $250.97   9.121%   $273.861   $273.86   $273.85   $273.90  
  Purchase #3 $163.47   13.316%   $185.2377   $185.24   $185.25   $185.20  
  Purchase #4 $55.81   7.563%   $60.0309   $60.03   $60.05   $60.00  
  Purchase #5 $14.46   9.693%   $15.8616   $15.86   $15.85   $15.90  
  Purchase #6 $96.87   9.425%   $106   $106.00   $106.00   $106.00  
  Purchase #7 $217.39   11.213%   $241.7659   $241.77   $241.75   $241.80  
  7 purchase totals = $1,019.89       $1,128.5483   $1,128.55   $1,128.55   $1,128.60