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 $75.84   13.619%   $86.1686   $86.17   $86.15   $86.20  
  Purchase #2 $124.46   11.140%   $138.3248   $138.32   $138.30   $138.30  
  Purchase #3 $55.57   4.794%   $58.234   $58.23   $58.25   $58.20  
  Purchase #4 $237.33   13.194%   $268.6433   $268.64   $268.65   $268.60  
  Purchase #5 $101.80   3.342%   $105.2022   $105.20   $105.20   $105.20  
  Purchase #6 $169.66   6.202%   $180.1823   $180.18   $180.20   $180.20  
  Purchase #7 $106.28   8.858%   $115.6943   $115.69   $115.70   $115.70  
  7 purchase totals = $870.94       $952.4495   $952.43   $952.45   $952.40