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 $66.88   5.212%   $70.3658   $70.37   $70.35   $70.40  
  Purchase #2 $248.61   8.468%   $269.6623   $269.66   $269.65   $269.70  
  Purchase #3 $236.57   4.727%   $247.7527   $247.75   $247.75   $247.80  
  Purchase #4 $88.91   3.473%   $91.9978   $92.00   $92.00   $92.00  
  Purchase #5 $172.36   12.691%   $194.2342   $194.23   $194.25   $194.20  
  Purchase #6 $37.83   12.442%   $42.5368   $42.54   $42.55   $42.50  
  Purchase #7 $226.46   4.455%   $236.5488   $236.55   $236.55   $236.50  
  7 purchase totals = $1,077.62       $1,153.0984   $1,153.10   $1,153.10   $1,153.10