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 $194.60   6.386%   $207.0272   $207.03   $207.05   $207.00  
  Purchase #2 $208.35   13.480%   $236.4356   $236.44   $236.45   $236.40  
  Purchase #3 $34.62   5.483%   $36.5182   $36.52   $36.50   $36.50  
  Purchase #4 $225.70   3.691%   $234.0306   $234.03   $234.05   $234.00  
  Purchase #5 $84.51   4.860%   $88.6172   $88.62   $88.60   $88.60  
  Purchase #6 $160.73   9.395%   $175.8306   $175.83   $175.85   $175.80  
  Purchase #7 $40.46   7.591%   $43.5313   $43.53   $43.55   $43.50  
  7 purchase totals = $948.97       $1,021.9907   $1,022.00   $1,022.05   $1,021.80