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 $68.78   8.464%   $74.6015   $74.60   $74.60   $74.60  
  Purchase #2 $56.58   4.356%   $59.0446   $59.04   $59.05   $59.00  
  Purchase #3 $143.96   5.111%   $151.3178   $151.32   $151.30   $151.30  
  Purchase #4 $227.54   4.109%   $236.8896   $236.89   $236.90   $236.90  
  Purchase #5 $42.61   3.299%   $44.0157   $44.02   $44.00   $44.00  
  Purchase #6 $58.42   5.621%   $61.7038   $61.70   $61.70   $61.70  
  Purchase #7 $189.44   12.272%   $212.6881   $212.69   $212.70   $212.70  
  7 purchase totals = $787.33       $840.2611   $840.26   $840.25   $840.20