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 $54.54   13.213%   $61.7464   $61.75   $61.75   $61.70  
  Purchase #2 $100.61   6.761%   $107.4122   $107.41   $107.40   $107.40  
  Purchase #3 $206.59   9.392%   $225.9929   $225.99   $226.00   $226.00  
  Purchase #4 $34.98   6.323%   $37.1918   $37.19   $37.20   $37.20  
  Purchase #5 $193.29   9.262%   $211.1925   $211.19   $211.20   $211.20  
  Purchase #6 $220.86   10.705%   $244.5031   $244.50   $244.50   $244.50  
  Purchase #7 $114.31   13.857%   $130.1499   $130.15   $130.15   $130.10  
  7 purchase totals = $925.18       $1,018.1888   $1,018.18   $1,018.20   $1,018.10