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 $191.67   4.654%   $200.5903   $200.59   $200.60   $200.60  
  Purchase #2 $126.88   6.293%   $134.8646   $134.86   $134.85   $134.90  
  Purchase #3 $10.77   12.561%   $12.1228   $12.12   $12.10   $12.10  
  Purchase #4 $109.62   7.212%   $117.5258   $117.53   $117.55   $117.50  
  Purchase #5 $29.91   4.212%   $31.1698   $31.17   $31.15   $31.20  
  Purchase #6 $136.52   3.143%   $140.8108   $140.81   $140.80   $140.80  
  Purchase #7 $224.47   9.824%   $246.5219   $246.52   $246.50   $246.50  
  7 purchase totals = $829.84       $883.6060   $883.60   $883.55   $883.60