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 $94.66   13.362%   $107.3085   $107.31   $107.30   $107.30  
  Purchase #2 $242.26   7.182%   $259.6591   $259.66   $259.65   $259.70  
  Purchase #3 $62.87   9.625%   $68.9212   $68.92   $68.90   $68.90  
  Purchase #4 $241.86   4.310%   $252.2842   $252.28   $252.30   $252.30  
  Purchase #5 $63.26   6.626%   $67.4516   $67.45   $67.45   $67.50  
  Purchase #6 $146.42   3.518%   $151.5711   $151.57   $151.55   $151.60  
  Purchase #7 $127.35   6.657%   $135.8277   $135.83   $135.85   $135.80  
  7 purchase totals = $978.68       $1,043.0234   $1,043.02   $1,043.00   $1,043.10