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 $27.96   4.347%   $29.1754   $29.18   $29.20   $29.20  
  Purchase #2 $235.54   13.146%   $266.5041   $266.50   $266.50   $266.50  
  Purchase #3 $82.99   11.544%   $92.5704   $92.57   $92.55   $92.60  
  Purchase #4 $227.42   9.116%   $248.1516   $248.15   $248.15   $248.20  
  Purchase #5 $85.60   9.183%   $93.4606   $93.46   $93.45   $93.50  
  Purchase #6 $64.79   12.161%   $72.6691   $72.67   $72.65   $72.70  
  Purchase #7 $210.50   4.564%   $220.1072   $220.11   $220.10   $220.10  
  7 purchase totals = $934.80       $1,022.6384   $1,022.64   $1,022.60   $1,022.80