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 $52.67   8.173%   $56.9747   $56.97   $56.95   $57.00  
  Purchase #2 $151.80   13.159%   $171.7754   $171.78   $171.80   $171.80  
  Purchase #3 $46.79   13.287%   $53.007   $53.01   $53.00   $53.00  
  Purchase #4 $94.84   9.373%   $103.7294   $103.73   $103.75   $103.70  
  Purchase #5 $121.91   9.720%   $133.7597   $133.76   $133.75   $133.80  
  Purchase #6 $236.65   12.749%   $266.8205   $266.82   $266.80   $266.80  
  Purchase #7 $198.29   11.221%   $220.5401   $220.54   $220.55   $220.50  
  7 purchase totals = $902.95       $1,006.6068   $1,006.61   $1,006.60   $1,006.60