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 $221.61   10.588%   $245.0741   $245.07   $245.05   $245.10  
  Purchase #2 $91.80   11.365%   $102.2331   $102.23   $102.25   $102.20  
  Purchase #3 $167.99   4.587%   $175.6957   $175.70   $175.70   $175.70  
  Purchase #4 $14.75   4.132%   $15.3595   $15.36   $15.35   $15.40  
  Purchase #5 $128.66   7.241%   $137.9763   $137.98   $138.00   $138.00  
  Purchase #6 $158.45   5.377%   $166.9699   $166.97   $166.95   $167.00  
  Purchase #7 $185.90   8.360%   $201.4412   $201.44   $201.45   $201.40  
  7 purchase totals = $969.16       $1,044.7498   $1,044.75   $1,044.75   $1,044.80