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 $161.98   12.696%   $182.545   $182.55   $182.55   $182.50  
  Purchase #2 $62.98   11.663%   $70.3254   $70.33   $70.35   $70.30  
  Purchase #3 $158.94   12.829%   $179.3304   $179.33   $179.35   $179.30  
  Purchase #4 $130.99   7.481%   $140.7894   $140.79   $140.80   $140.80  
  Purchase #5 $248.72   8.537%   $269.9532   $269.95   $269.95   $270.00  
  Purchase #6 $140.28   11.813%   $156.8513   $156.85   $156.85   $156.90  
  Purchase #7 $221.82   5.279%   $233.5299   $233.53   $233.55   $233.50  
  7 purchase totals = $1,125.71       $1,233.3246   $1,233.33   $1,233.40   $1,233.30