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 $71.54   7.174%   $76.6723   $76.67   $76.65   $76.70  
  Purchase #2 $147.28   11.731%   $164.5574   $164.56   $164.55   $164.60  
  Purchase #3 $136.68   4.848%   $143.3062   $143.31   $143.30   $143.30  
  Purchase #4 $187.44   13.488%   $212.7219   $212.72   $212.70   $212.70  
  Purchase #5 $233.46   12.798%   $263.3382   $263.34   $263.35   $263.30  
  Purchase #6 $21.58   5.132%   $22.6875   $22.69   $22.70   $22.70  
  Purchase #7 $178.54   3.168%   $184.1961   $184.20   $184.20   $184.20  
  7 purchase totals = $976.52       $1,067.4796   $1,067.49   $1,067.45   $1,067.50