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 $75.85   3.701%   $78.6572   $78.66   $78.65   $78.70  
  Purchase #2 $227.85   7.164%   $244.1732   $244.17   $244.15   $244.20  
  Purchase #3 $5.42   11.207%   $6.0274   $6.03   $6.05   $6.00  
  Purchase #4 $61.52   11.655%   $68.6902   $68.69   $68.70   $68.70  
  Purchase #5 $176.37   8.195%   $190.8235   $190.82   $190.80   $190.80  
  Purchase #6 $176.76   12.242%   $198.399   $198.40   $198.40   $198.40  
  Purchase #7 $209.76   8.604%   $227.8078   $227.81   $227.80   $227.80  
  7 purchase totals = $933.53       $1,014.5783   $1,014.58   $1,014.55   $1,014.60