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 $48.88   6.129%   $51.8759   $51.88   $51.90   $51.90  
  Purchase #2 $241.55   10.866%   $267.7968   $267.80   $267.80   $267.80  
  Purchase #3 $104.62   9.446%   $114.5024   $114.50   $114.50   $114.50  
  Purchase #4 $235.60   9.759%   $258.5922   $258.59   $258.60   $258.60  
  Purchase #5 $228.80   4.252%   $238.5286   $238.53   $238.55   $238.50  
  Purchase #6 $105.68   13.859%   $120.3262   $120.33   $120.35   $120.30  
  Purchase #7 $142.30   8.304%   $154.1166   $154.12   $154.10   $154.10  
  7 purchase totals = $1,107.43       $1,205.7387   $1,205.75   $1,205.80   $1,205.70