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 $219.48   3.694%   $227.5876   $227.59   $227.60   $227.60  
  Purchase #2 $104.99   8.227%   $113.6275   $113.63   $113.65   $113.60  
  Purchase #3 $113.26   3.453%   $117.1709   $117.17   $117.15   $117.20  
  Purchase #4 $59.29   7.116%   $63.5091   $63.51   $63.50   $63.50  
  Purchase #5 $186.92   13.265%   $211.7149   $211.71   $211.70   $211.70  
  Purchase #6 $204.93   12.362%   $230.2634   $230.26   $230.25   $230.30  
  Purchase #7 $69.81   7.196%   $74.8335   $74.83   $74.85   $74.80  
  7 purchase totals = $958.68       $1,038.7069   $1,038.70   $1,038.70   $1,038.70