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 $218.95   11.322%   $243.7395   $243.74   $243.75   $243.70  
  Purchase #2 $213.97   8.342%   $231.8194   $231.82   $231.80   $231.80  
  Purchase #3 $13.26   12.258%   $14.8854   $14.89   $14.90   $14.90  
  Purchase #4 $209.45   11.387%   $233.3001   $233.30   $233.30   $233.30  
  Purchase #5 $230.35   8.167%   $249.1627   $249.16   $249.15   $249.20  
  Purchase #6 $184.27   3.765%   $191.2078   $191.21   $191.20   $191.20  
  Purchase #7 $89.61   9.853%   $98.4393   $98.44   $98.45   $98.40  
  7 purchase totals = $1,159.86       $1,262.5542   $1,262.56   $1,262.55   $1,262.50