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 $88.42   8.145%   $95.6218   $95.62   $95.60   $95.60  
  Purchase #2 $163.99   5.151%   $172.4371   $172.44   $172.45   $172.40  
  Purchase #3 $32.96   11.747%   $36.8318   $36.83   $36.85   $36.80  
  Purchase #4 $189.76   11.283%   $211.1706   $211.17   $211.15   $211.20  
  Purchase #5 $212.92   10.193%   $234.6229   $234.62   $234.60   $234.60  
  Purchase #6 $117.25   13.865%   $133.5067   $133.51   $133.50   $133.50  
  Purchase #7 $36.70   6.646%   $39.1391   $39.14   $39.15   $39.10  
  7 purchase totals = $842.00       $923.3300   $923.33   $923.30   $923.20