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 $82.58   3.162%   $85.1912   $85.19   $85.20   $85.20  
  Purchase #2 $237.69   8.310%   $257.442   $257.44   $257.45   $257.40  
  Purchase #3 $86.73   10.715%   $96.0231   $96.02   $96.00   $96.00  
  Purchase #4 $8.81   8.278%   $9.5393   $9.54   $9.55   $9.50  
  Purchase #5 $113.94   7.603%   $122.6029   $122.60   $122.60   $122.60  
  Purchase #6 $165.26   6.467%   $175.9474   $175.95   $175.95   $175.90  
  Purchase #7 $236.50   12.414%   $265.8591   $265.86   $265.85   $265.90  
  7 purchase totals = $931.51       $1,012.6050   $1,012.60   $1,012.60   $1,012.50