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 $205.46   3.136%   $211.9032   $211.90   $211.90   $211.90  
  Purchase #2 $44.64   4.560%   $46.6756   $46.68   $46.70   $46.70  
  Purchase #3 $235.26   6.193%   $249.8297   $249.83   $249.85   $249.80  
  Purchase #4 $172.59   9.834%   $189.5625   $189.56   $189.55   $189.60  
  Purchase #5 $14.86   4.522%   $15.532   $15.53   $15.55   $15.50  
  Purchase #6 $37.48   11.863%   $41.9263   $41.93   $41.95   $41.90  
  Purchase #7 $96.66   6.121%   $102.5766   $102.58   $102.60   $102.60  
  7 purchase totals = $806.95       $858.0059   $858.01   $858.10   $858.00