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 $13.70   8.832%   $14.91   $14.91   $14.90   $14.90  
  Purchase #2 $190.39   13.475%   $216.0451   $216.05   $216.05   $216.00  
  Purchase #3 $47.77   11.386%   $53.2091   $53.21   $53.20   $53.20  
  Purchase #4 $68.67   12.433%   $77.2077   $77.21   $77.20   $77.20  
  Purchase #5 $222.89   3.832%   $231.4311   $231.43   $231.45   $231.40  
  Purchase #6 $35.94   7.829%   $38.7537   $38.75   $38.75   $38.80  
  Purchase #7 $63.64   10.315%   $70.2045   $70.20   $70.20   $70.20  
  7 purchase totals = $643.00       $701.7612   $701.76   $701.75   $701.70