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 $248.37   11.416%   $276.7239   $276.72   $276.70   $276.70  
  Purchase #2 $189.25   6.329%   $201.2276   $201.23   $201.25   $201.20  
  Purchase #3 $44.92   8.720%   $48.837   $48.84   $48.85   $48.80  
  Purchase #4 $242.66   8.671%   $263.701   $263.70   $263.70   $263.70  
  Purchase #5 $113.31   13.699%   $128.8323   $128.83   $128.85   $128.80  
  Purchase #6 $179.35   8.106%   $193.8881   $193.89   $193.90   $193.90  
  Purchase #7 $225.39   5.402%   $237.5656   $237.57   $237.55   $237.60  
  7 purchase totals = $1,243.25       $1,350.7755   $1,350.78   $1,350.80   $1,350.70