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 $67.33   3.412%   $69.6273   $69.63   $69.65   $69.60  
  Purchase #2 $122.95   7.267%   $131.8848   $131.88   $131.90   $131.90  
  Purchase #3 $183.93   3.690%   $190.717   $190.72   $190.70   $190.70  
  Purchase #4 $241.46   5.156%   $253.9097   $253.91   $253.90   $253.90  
  Purchase #5 $73.66   8.829%   $80.1634   $80.16   $80.15   $80.20  
  Purchase #6 $109.82   3.653%   $113.8317   $113.83   $113.85   $113.80  
  Purchase #7 $163.33   3.731%   $169.4238   $169.42   $169.40   $169.40  
  7 purchase totals = $962.48       $1,009.5577   $1,009.55   $1,009.55   $1,009.50