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 $158.68   10.196%   $174.859   $174.86   $174.85   $174.90  
  Purchase #2 $155.34   9.556%   $170.1843   $170.18   $170.20   $170.20  
  Purchase #3 $12.90   5.667%   $13.631   $13.63   $13.65   $13.60  
  Purchase #4 $93.25   6.824%   $99.6134   $99.61   $99.60   $99.60  
  Purchase #5 $116.82   3.353%   $120.737   $120.74   $120.75   $120.70  
  Purchase #6 $208.99   7.598%   $224.8691   $224.87   $224.85   $224.90  
  Purchase #7 $240.33   13.681%   $273.2095   $273.21   $273.20   $273.20  
  7 purchase totals = $986.31       $1,077.1033   $1,077.10   $1,077.10   $1,077.10