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 $54.96   3.267%   $56.7555   $56.76   $56.75   $56.80  
  Purchase #2 $211.48   9.449%   $231.4627   $231.46   $231.45   $231.50  
  Purchase #3 $186.57   5.432%   $196.7045   $196.70   $196.70   $196.70  
  Purchase #4 $156.41   10.175%   $172.3247   $172.32   $172.30   $172.30  
  Purchase #5 $19.48   12.565%   $21.9277   $21.93   $21.95   $21.90  
  Purchase #6 $176.43   9.785%   $193.6937   $193.69   $193.70   $193.70  
  Purchase #7 $144.28   3.474%   $149.2923   $149.29   $149.30   $149.30  
  7 purchase totals = $949.61       $1,022.1611   $1,022.15   $1,022.15   $1,022.20