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 $38.53   7.205%   $41.3061   $41.31   $41.30   $41.30  
  Purchase #2 $114.60   10.778%   $126.9516   $126.95   $126.95   $127.00  
  Purchase #3 $68.43   4.345%   $71.4033   $71.40   $71.40   $71.40  
  Purchase #4 $231.84   3.417%   $239.762   $239.76   $239.75   $239.80  
  Purchase #5 $176.48   7.300%   $189.363   $189.36   $189.35   $189.40  
  Purchase #6 $211.94   5.664%   $223.9443   $223.94   $223.95   $223.90  
  Purchase #7 $112.74   8.428%   $122.2417   $122.24   $122.25   $122.20  
  7 purchase totals = $954.56       $1,014.9720   $1,014.96   $1,014.95   $1,015.00