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 $32.61   6.597%   $34.7613   $34.76   $34.75   $34.80  
  Purchase #2 $184.33   7.596%   $198.3317   $198.33   $198.35   $198.30  
  Purchase #3 $230.88   8.606%   $250.7495   $250.75   $250.75   $250.70  
  Purchase #4 $128.34   11.243%   $142.7693   $142.77   $142.75   $142.80  
  Purchase #5 $126.52   3.482%   $130.9254   $130.93   $130.95   $130.90  
  Purchase #6 $246.25   6.723%   $262.8054   $262.81   $262.80   $262.80  
  Purchase #7 $9.49   6.425%   $10.0997   $10.10   $10.10   $10.10  
  7 purchase totals = $958.42       $1,030.4423   $1,030.45   $1,030.45   $1,030.40