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 $84.56   8.314%   $91.5903   $91.59   $91.60   $91.60  
  Purchase #2 $164.66   5.287%   $173.3656   $173.37   $173.35   $173.40  
  Purchase #3 $48.58   9.167%   $53.0333   $53.03   $53.05   $53.00  
  Purchase #4 $230.65   4.810%   $241.7443   $241.74   $241.75   $241.70  
  Purchase #5 $140.93   6.857%   $150.5936   $150.59   $150.60   $150.60  
  Purchase #6 $236.26   12.196%   $265.0743   $265.07   $265.05   $265.10  
  Purchase #7 $236.48   4.103%   $246.1828   $246.18   $246.20   $246.20  
  7 purchase totals = $1,142.12       $1,221.5842   $1,221.57   $1,221.60   $1,221.60