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 $153.65   6.353%   $163.4114   $163.41   $163.40   $163.40  
  Purchase #2 $12.82   11.167%   $14.2516   $14.25   $14.25   $14.30  
  Purchase #3 $117.59   6.833%   $125.6249   $125.62   $125.60   $125.60  
  Purchase #4 $24.49   3.368%   $25.3148   $25.31   $25.30   $25.30  
  Purchase #5 $205.41   10.799%   $227.5922   $227.59   $227.60   $227.60  
  Purchase #6 $145.66   12.812%   $164.322   $164.32   $164.30   $164.30  
  Purchase #7 $67.83   5.412%   $71.501   $71.50   $71.50   $71.50  
  7 purchase totals = $727.45       $792.0179   $792.00   $791.95   $792.00