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 $60.50   9.399%   $66.1864   $66.19   $66.20   $66.20  
  Purchase #2 $210.26   12.202%   $235.9159   $235.92   $235.90   $235.90  
  Purchase #3 $231.57   3.836%   $240.453   $240.45   $240.45   $240.50  
  Purchase #4 $61.92   12.545%   $69.6879   $69.69   $69.70   $69.70  
  Purchase #5 $177.86   8.253%   $192.5388   $192.54   $192.55   $192.50  
  Purchase #6 $5.26   11.626%   $5.8715   $5.87   $5.85   $5.90  
  Purchase #7 $210.98   12.161%   $236.6373   $236.64   $236.65   $236.60  
  7 purchase totals = $958.35       $1,047.2908   $1,047.30   $1,047.30   $1,047.30