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 $70.41   5.276%   $74.1248   $74.12   $74.10   $74.10  
  Purchase #2 $216.92   4.841%   $227.4211   $227.42   $227.40   $227.40  
  Purchase #3 $176.43   9.126%   $192.531   $192.53   $192.55   $192.50  
  Purchase #4 $108.72   12.209%   $121.9936   $121.99   $122.00   $122.00  
  Purchase #5 $205.66   9.656%   $225.5185   $225.52   $225.50   $225.50  
  Purchase #6 $148.28   13.776%   $168.7071   $168.71   $168.70   $168.70  
  Purchase #7 $225.84   10.700%   $250.0049   $250.00   $250.00   $250.00  
  7 purchase totals = $1,152.26       $1,260.3010   $1,260.29   $1,260.25   $1,260.20