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 $63.34   10.568%   $70.0338   $70.03   $70.05   $70.00  
  Purchase #2 $211.83   4.338%   $221.0192   $221.02   $221.00   $221.00  
  Purchase #3 $66.53   4.466%   $69.5012   $69.50   $69.50   $69.50  
  Purchase #4 $222.82   5.608%   $235.3157   $235.32   $235.30   $235.30  
  Purchase #5 $118.56   13.775%   $134.8916   $134.89   $134.90   $134.90  
  Purchase #6 $241.71   13.498%   $274.336   $274.34   $274.35   $274.30  
  Purchase #7 $126.69   6.171%   $134.508   $134.51   $134.50   $134.50  
  7 purchase totals = $1,051.48       $1,139.6055   $1,139.61   $1,139.60   $1,139.50