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 $247.96   9.779%   $272.208   $272.21   $272.20   $272.20  
  Purchase #2 $196.56   9.386%   $215.0091   $215.01   $215.00   $215.00  
  Purchase #3 $17.51   13.455%   $19.866   $19.87   $19.85   $19.90  
  Purchase #4 $232.78   5.441%   $245.4456   $245.45   $245.45   $245.40  
  Purchase #5 $115.56   10.683%   $127.9053   $127.91   $127.90   $127.90  
  Purchase #6 $133.61   8.770%   $145.3276   $145.33   $145.35   $145.30  
  Purchase #7 $119.86   11.363%   $133.4797   $133.48   $133.50   $133.50  
  7 purchase totals = $1,063.84       $1,159.2413   $1,159.26   $1,159.25   $1,159.20