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 $141.57   8.204%   $153.1844   $153.18   $153.20   $153.20  
  Purchase #2 $234.86   9.711%   $257.6673   $257.67   $257.65   $257.70  
  Purchase #3 $139.59   12.411%   $156.9145   $156.91   $156.90   $156.90  
  Purchase #4 $214.80   9.205%   $234.5723   $234.57   $234.55   $234.60  
  Purchase #5 $170.67   9.500%   $186.8837   $186.88   $186.90   $186.90  
  Purchase #6 $174.63   12.639%   $196.7015   $196.70   $196.70   $196.70  
  Purchase #7 $109.30   6.318%   $116.2056   $116.21   $116.20   $116.20  
  7 purchase totals = $1,185.42       $1,302.1293   $1,302.12   $1,302.10   $1,302.20