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 $40.44   7.739%   $43.5697   $43.57   $43.55   $43.60  
  Purchase #2 $115.95   4.293%   $120.9277   $120.93   $120.95   $120.90  
  Purchase #3 $17.30   10.354%   $19.0912   $19.09   $19.10   $19.10  
  Purchase #4 $41.61   11.653%   $46.4588   $46.46   $46.45   $46.50  
  Purchase #5 $203.86   7.675%   $219.5063   $219.51   $219.50   $219.50  
  Purchase #6 $58.62   8.366%   $63.5241   $63.52   $63.50   $63.50  
  Purchase #7 $204.77   6.851%   $218.7988   $218.80   $218.80   $218.80  
  7 purchase totals = $682.55       $731.8766   $731.88   $731.85   $731.90