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 $32.32   10.688%   $35.7744   $35.77   $35.75   $35.80  
  Purchase #2 $245.55   6.710%   $262.0264   $262.03   $262.05   $262.00  
  Purchase #3 $172.48   4.104%   $179.5586   $179.56   $179.55   $179.60  
  Purchase #4 $35.97   4.349%   $37.5343   $37.53   $37.55   $37.50  
  Purchase #5 $153.63   11.135%   $170.7367   $170.74   $170.75   $170.70  
  Purchase #6 $86.64   9.577%   $94.9375   $94.94   $94.95   $94.90  
  Purchase #7 $63.98   5.696%   $67.6243   $67.62   $67.60   $67.60  
  7 purchase totals = $790.57       $848.1922   $848.19   $848.20   $848.10