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 $245.54   4.790%   $257.3014   $257.30   $257.30   $257.30  
  Purchase #2 $82.39   8.340%   $89.2613   $89.26   $89.25   $89.30  
  Purchase #3 $23.46   10.651%   $25.9587   $25.96   $25.95   $26.00  
  Purchase #4 $243.57   4.249%   $253.9193   $253.92   $253.90   $253.90  
  Purchase #5 $126.56   6.146%   $134.3384   $134.34   $134.35   $134.30  
  Purchase #6 $133.76   6.369%   $142.2792   $142.28   $142.30   $142.30  
  Purchase #7 $159.34   4.544%   $166.5804   $166.58   $166.60   $166.60  
  7 purchase totals = $1,014.62       $1,069.6387   $1,069.64   $1,069.65   $1,069.70