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 $207.71   4.380%   $216.8077   $216.81   $216.80   $216.80  
  Purchase #2 $62.26   7.379%   $66.8542   $66.85   $66.85   $66.90  
  Purchase #3 $80.33   3.258%   $82.9472   $82.95   $82.95   $82.90  
  Purchase #4 $148.85   9.139%   $162.4534   $162.45   $162.45   $162.50  
  Purchase #5 $186.82   3.651%   $193.6408   $193.64   $193.65   $193.60  
  Purchase #6 $62.54   11.853%   $69.9529   $69.95   $69.95   $70.00  
  Purchase #7 $236.67   6.871%   $252.9316   $252.93   $252.95   $252.90  
  7 purchase totals = $985.18       $1,045.5878   $1,045.58   $1,045.60   $1,045.60