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 $61.50   11.218%   $68.3991   $68.40   $68.40   $68.40  
  Purchase #2 $144.42   13.315%   $163.6495   $163.65   $163.65   $163.60  
  Purchase #3 $86.46   10.739%   $95.7449   $95.74   $95.75   $95.70  
  Purchase #4 $59.67   5.778%   $63.1177   $63.12   $63.10   $63.10  
  Purchase #5 $95.94   13.156%   $108.5619   $108.56   $108.55   $108.60  
  Purchase #6 $13.50   7.503%   $14.5129   $14.51   $14.50   $14.50  
  Purchase #7 $165.87   4.111%   $172.6889   $172.69   $172.70   $172.70  
  7 purchase totals = $627.36       $686.6749   $686.67   $686.65   $686.60