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 $50.57   3.834%   $52.5089   $52.51   $52.50   $52.50  
  Purchase #2 $211.93   11.689%   $236.7025   $236.70   $236.70   $236.70  
  Purchase #3 $66.97   4.373%   $69.8986   $69.90   $69.90   $69.90  
  Purchase #4 $229.48   11.665%   $256.2488   $256.25   $256.25   $256.20  
  Purchase #5 $214.94   9.811%   $236.0278   $236.03   $236.05   $236.00  
  Purchase #6 $216.83   5.850%   $229.5146   $229.51   $229.50   $229.50  
  Purchase #7 $177.31   4.839%   $185.89   $185.89   $185.90   $185.90  
  7 purchase totals = $1,168.03       $1,266.7912   $1,266.79   $1,266.80   $1,266.70