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 $135.68   11.181%   $150.8504   $150.85   $150.85   $150.90  
  Purchase #2 $130.80   9.842%   $143.6733   $143.67   $143.65   $143.70  
  Purchase #3 $248.84   11.623%   $277.7627   $277.76   $277.75   $277.80  
  Purchase #4 $68.77   3.655%   $71.2835   $71.28   $71.30   $71.30  
  Purchase #5 $96.63   9.773%   $106.0736   $106.07   $106.05   $106.10  
  Purchase #6 $245.37   6.490%   $261.2945   $261.29   $261.30   $261.30  
  Purchase #7 $241.76   6.149%   $256.6258   $256.63   $256.65   $256.60  
  7 purchase totals = $1,167.85       $1,267.5638   $1,267.55   $1,267.55   $1,267.70