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 $65.89   11.133%   $73.2255   $73.23   $73.25   $73.20  
  Purchase #2 $233.76   6.449%   $248.8352   $248.84   $248.85   $248.80  
  Purchase #3 $229.96   6.607%   $245.1535   $245.15   $245.15   $245.20  
  Purchase #4 $26.80   11.340%   $29.8391   $29.84   $29.85   $29.80  
  Purchase #5 $249.58   9.167%   $272.459   $272.46   $272.45   $272.50  
  Purchase #6 $103.62   11.449%   $115.4835   $115.48   $115.50   $115.50  
  Purchase #7 $167.99   7.802%   $181.0966   $181.10   $181.10   $181.10  
  7 purchase totals = $1,077.60       $1,166.0924   $1,166.10   $1,166.15   $1,166.10