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 $218.29   10.673%   $241.5881   $241.59   $241.60   $241.60  
  Purchase #2 $23.40   11.626%   $26.1205   $26.12   $26.10   $26.10  
  Purchase #3 $110.70   6.359%   $117.7394   $117.74   $117.75   $117.70  
  Purchase #4 $230.34   4.863%   $241.5414   $241.54   $241.55   $241.50  
  Purchase #5 $88.49   6.118%   $93.9038   $93.90   $93.90   $93.90  
  Purchase #6 $163.94   6.414%   $174.4551   $174.46   $174.45   $174.50  
  Purchase #7 $105.53   5.126%   $110.9395   $110.94   $110.95   $110.90  
  7 purchase totals = $940.69       $1,006.2878   $1,006.29   $1,006.30   $1,006.20