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 $186.29   3.195%   $192.242   $192.24   $192.25   $192.20  
  Purchase #2 $37.97   13.551%   $43.1153   $43.12   $43.10   $43.10  
  Purchase #3 $229.89   3.489%   $237.9109   $237.91   $237.90   $237.90  
  Purchase #4 $44.77   5.766%   $47.3514   $47.35   $47.35   $47.40  
  Purchase #5 $168.49   4.272%   $175.6879   $175.69   $175.70   $175.70  
  Purchase #6 $99.94   6.125%   $106.0613   $106.06   $106.05   $106.10  
  Purchase #7 $64.49   6.155%   $68.4594   $68.46   $68.45   $68.50  
  7 purchase totals = $831.84       $870.8282   $870.83   $870.80   $870.90