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 $6.88   10.282%   $7.5874   $7.59   $7.60   $7.60  
  Purchase #2 $60.62   8.108%   $65.5351   $65.54   $65.55   $65.50  
  Purchase #3 $54.91   10.351%   $60.5937   $60.59   $60.60   $60.60  
  Purchase #4 $37.83   4.356%   $39.4779   $39.48   $39.50   $39.50  
  Purchase #5 $58.53   7.873%   $63.1381   $63.14   $63.15   $63.10  
  Purchase #6 $53.62   5.282%   $56.4522   $56.45   $56.45   $56.50  
  Purchase #7 $71.36   5.314%   $75.1521   $75.15   $75.15   $75.20  
  7 purchase totals = $343.75       $367.9365   $367.94   $368.00   $368.00