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 $61.59   3.146%   $63.5276   $63.53   $63.55   $63.50  
  Purchase #2 $125.99   11.272%   $140.1916   $140.19   $140.20   $140.20  
  Purchase #3 $17.63   6.585%   $18.7909   $18.79   $18.80   $18.80  
  Purchase #4 $35.99   3.162%   $37.128   $37.13   $37.15   $37.10  
  Purchase #5 $93.93   8.624%   $102.0305   $102.03   $102.05   $102.00  
  Purchase #6 $212.69   6.267%   $226.0193   $226.02   $226.00   $226.00  
  Purchase #7 $94.67   11.381%   $105.4444   $105.44   $105.45   $105.40  
  7 purchase totals = $642.49       $693.1323   $693.13   $693.20   $693.00