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 $226.81   5.521%   $239.3322   $239.33   $239.35   $239.30  
  Purchase #2 $51.46   3.348%   $53.1829   $53.18   $53.20   $53.20  
  Purchase #3 $152.44   3.491%   $157.7617   $157.76   $157.75   $157.80  
  Purchase #4 $250.46   7.346%   $268.8588   $268.86   $268.85   $268.90  
  Purchase #5 $200.56   5.323%   $211.2358   $211.24   $211.25   $211.20  
  Purchase #6 $209.85   4.587%   $219.4758   $219.48   $219.50   $219.50  
  Purchase #7 $212.53   6.137%   $225.573   $225.57   $225.55   $225.60  
  7 purchase totals = $1,304.11       $1,375.4202   $1,375.42   $1,375.45   $1,375.50