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 $87.92   12.189%   $98.6366   $98.64   $98.65   $98.60  
  Purchase #2 $53.89   6.574%   $57.4327   $57.43   $57.45   $57.40  
  Purchase #3 $226.36   6.629%   $241.3654   $241.37   $241.35   $241.40  
  Purchase #4 $168.62   5.375%   $177.6833   $177.68   $177.70   $177.70  
  Purchase #5 $35.33   6.508%   $37.6293   $37.63   $37.65   $37.60  
  Purchase #6 $52.64   6.253%   $55.9316   $55.93   $55.95   $55.90  
  Purchase #7 $40.53   6.469%   $43.1519   $43.15   $43.15   $43.20  
  7 purchase totals = $665.29       $711.8308   $711.83   $711.90   $711.80