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 $52.71   11.138%   $58.5808   $58.58   $58.60   $58.60  
  Purchase #2 $63.61   3.370%   $65.7537   $65.75   $65.75   $65.80  
  Purchase #3 $147.83   5.286%   $155.6443   $155.64   $155.65   $155.60  
  Purchase #4 $37.30   5.680%   $39.4186   $39.42   $39.40   $39.40  
  Purchase #5 $119.50   11.159%   $132.835   $132.84   $132.85   $132.80  
  Purchase #6 $67.41   10.601%   $74.5561   $74.56   $74.55   $74.60  
  Purchase #7 $164.92   5.863%   $174.5893   $174.59   $174.60   $174.60  
  7 purchase totals = $653.28       $701.3778   $701.38   $701.40   $701.40