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 $59.79   5.705%   $63.201   $63.20   $63.20   $63.20  
  Purchase #2 $108.55   4.716%   $113.6692   $113.67   $113.65   $113.70  
  Purchase #3 $63.84   9.195%   $69.7101   $69.71   $69.70   $69.70  
  Purchase #4 $249.39   12.861%   $281.464   $281.46   $281.45   $281.50  
  Purchase #5 $164.43   11.806%   $183.8426   $183.84   $183.85   $183.80  
  Purchase #6 $165.63   7.589%   $178.1997   $178.20   $178.20   $178.20  
  Purchase #7 $129.82   13.743%   $147.6612   $147.66   $147.65   $147.70  
  7 purchase totals = $941.45       $1,037.7478   $1,037.74   $1,037.70   $1,037.80