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 $224.79   12.788%   $253.5361   $253.54   $253.55   $253.50  
  Purchase #2 $222.95   6.600%   $237.6647   $237.66   $237.65   $237.70  
  Purchase #3 $68.58   11.372%   $76.3789   $76.38   $76.40   $76.40  
  Purchase #4 $227.99   4.498%   $238.245   $238.25   $238.25   $238.20  
  Purchase #5 $190.59   7.501%   $204.8862   $204.89   $204.90   $204.90  
  Purchase #6 $150.90   8.359%   $163.5137   $163.51   $163.50   $163.50  
  Purchase #7 $175.52   4.542%   $183.4921   $183.49   $183.50   $183.50  
  7 purchase totals = $1,261.32       $1,357.7167   $1,357.72   $1,357.75   $1,357.70