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 $46.35   13.531%   $52.6216   $52.62   $52.60   $52.60  
  Purchase #2 $48.29   7.604%   $51.962   $51.96   $51.95   $52.00  
  Purchase #3 $114.89   13.576%   $130.4875   $130.49   $130.50   $130.50  
  Purchase #4 $60.90   9.331%   $66.5826   $66.58   $66.60   $66.60  
  Purchase #5 $228.50   8.124%   $247.0633   $247.06   $247.05   $247.10  
  Purchase #6 $243.84   8.592%   $264.7907   $264.79   $264.80   $264.80  
  Purchase #7 $241.38   8.248%   $261.289   $261.29   $261.30   $261.30  
  7 purchase totals = $984.15       $1,074.7967   $1,074.79   $1,074.80   $1,074.90