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 $173.55   3.844%   $180.2213   $180.22   $180.20   $180.20  
  Purchase #2 $9.57   3.740%   $9.9279   $9.93   $9.95   $9.90  
  Purchase #3 $48.62   8.312%   $52.6613   $52.66   $52.65   $52.70  
  Purchase #4 $129.39   4.188%   $134.8089   $134.81   $134.80   $134.80  
  Purchase #5 $60.88   4.390%   $63.5526   $63.55   $63.55   $63.60  
  Purchase #6 $142.92   10.695%   $158.2053   $158.21   $158.20   $158.20  
  Purchase #7 $59.57   5.333%   $62.7469   $62.75   $62.75   $62.70  
  7 purchase totals = $624.50       $662.1242   $662.13   $662.10   $662.10