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 $43.42   13.247%   $49.1718   $49.17   $49.15   $49.20  
  Purchase #2 $240.79   4.459%   $251.5268   $251.53   $251.55   $251.50  
  Purchase #3 $144.36   10.461%   $159.4615   $159.46   $159.45   $159.50  
  Purchase #4 $58.33   13.835%   $66.4   $66.40   $66.40   $66.40  
  Purchase #5 $246.40   8.814%   $268.1177   $268.12   $268.10   $268.10  
  Purchase #6 $127.61   10.759%   $141.3396   $141.34   $141.35   $141.30  
  Purchase #7 $64.34   4.118%   $66.9895   $66.99   $67.00   $67.00  
  7 purchase totals = $925.25       $1,003.0069   $1,003.01   $1,003.00   $1,003.00