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 $228.97   8.574%   $248.6019   $248.60   $248.60   $248.60  
  Purchase #2 $152.29   8.188%   $164.7595   $164.76   $164.75   $164.80  
  Purchase #3 $71.85   12.399%   $80.7587   $80.76   $80.75   $80.80  
  Purchase #4 $127.98   5.537%   $135.0663   $135.07   $135.05   $135.10  
  Purchase #5 $111.53   4.403%   $116.4407   $116.44   $116.45   $116.40  
  Purchase #6 $203.48   4.753%   $213.1514   $213.15   $213.15   $213.20  
  Purchase #7 $70.94   10.767%   $78.5781   $78.58   $78.60   $78.60  
  7 purchase totals = $967.04       $1,037.3566   $1,037.36   $1,037.35   $1,037.50