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 $52.46   12.629%   $59.0852   $59.09   $59.10   $59.10  
  Purchase #2 $211.39   8.712%   $229.8063   $229.81   $229.80   $229.80  
  Purchase #3 $91.44   11.434%   $101.8952   $101.90   $101.90   $101.90  
  Purchase #4 $214.42   5.490%   $226.1917   $226.19   $226.20   $226.20  
  Purchase #5 $205.99   12.227%   $231.1764   $231.18   $231.20   $231.20  
  Purchase #6 $96.64   8.726%   $105.0728   $105.07   $105.05   $105.10  
  Purchase #7 $39.30   13.531%   $44.6177   $44.62   $44.60   $44.60  
  7 purchase totals = $911.64       $997.8453   $997.86   $997.85   $997.90