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 $58.35   12.675%   $65.7459   $65.75   $65.75   $65.70  
  Purchase #2 $158.35   8.340%   $171.5564   $171.56   $171.55   $171.60  
  Purchase #3 $40.60   3.584%   $42.0551   $42.06   $42.05   $42.10  
  Purchase #4 $197.79   9.753%   $217.0805   $217.08   $217.10   $217.10  
  Purchase #5 $243.32   12.874%   $274.645   $274.65   $274.65   $274.60  
  Purchase #6 $50.60   4.866%   $53.0622   $53.06   $53.05   $53.10  
  Purchase #7 $198.48   9.537%   $217.409   $217.41   $217.40   $217.40  
  7 purchase totals = $947.49       $1,041.5541   $1,041.57   $1,041.55   $1,041.60