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 $169.29   8.525%   $183.722   $183.72   $183.70   $183.70  
  Purchase #2 $5.98   7.512%   $6.4292   $6.43   $6.45   $6.40  
  Purchase #3 $124.56   4.770%   $130.5015   $130.50   $130.50   $130.50  
  Purchase #4 $232.97   8.450%   $252.656   $252.66   $252.65   $252.70  
  Purchase #5 $180.92   10.330%   $199.609   $199.61   $199.60   $199.60  
  Purchase #6 $129.59   8.403%   $140.4794   $140.48   $140.50   $140.50  
  Purchase #7 $129.54   7.691%   $139.5029   $139.50   $139.50   $139.50  
  7 purchase totals = $972.85       $1,052.9000   $1,052.90   $1,052.90   $1,052.90