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 $32.86   4.858%   $34.4563   $34.46   $34.45   $34.50  
  Purchase #2 $249.42   12.751%   $281.2235   $281.22   $281.20   $281.20  
  Purchase #3 $245.83   9.576%   $269.3707   $269.37   $269.35   $269.40  
  Purchase #4 $102.60   12.654%   $115.583   $115.58   $115.60   $115.60  
  Purchase #5 $161.93   5.330%   $170.5609   $170.56   $170.55   $170.60  
  Purchase #6 $212.29   5.273%   $223.4841   $223.48   $223.50   $223.50  
  Purchase #7 $231.72   7.134%   $248.2509   $248.25   $248.25   $248.30  
  7 purchase totals = $1,236.65       $1,342.9294   $1,342.92   $1,342.90   $1,343.10