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 $142.96   5.673%   $151.0701   $151.07   $151.05   $151.10  
  Purchase #2 $63.97   3.143%   $65.9806   $65.98   $66.00   $66.00  
  Purchase #3 $177.94   13.303%   $201.6114   $201.61   $201.60   $201.60  
  Purchase #4 $131.74   7.739%   $141.9354   $141.94   $141.95   $141.90  
  Purchase #5 $21.28   3.873%   $22.1042   $22.10   $22.10   $22.10  
  Purchase #6 $189.81   10.747%   $210.2089   $210.21   $210.20   $210.20  
  Purchase #7 $225.33   13.381%   $255.4814   $255.48   $255.50   $255.50  
  7 purchase totals = $953.03       $1,048.3920   $1,048.39   $1,048.40   $1,048.40