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 $164.31   11.822%   $183.7347   $183.73   $183.75   $183.70  
  Purchase #2 $153.60   6.675%   $163.8528   $163.85   $163.85   $163.90  
  Purchase #3 $105.77   3.403%   $109.3694   $109.37   $109.35   $109.40  
  Purchase #4 $46.30   3.466%   $47.9048   $47.90   $47.90   $47.90  
  Purchase #5 $86.80   11.666%   $96.9261   $96.93   $96.95   $96.90  
  Purchase #6 $161.33   7.824%   $173.9525   $173.95   $173.95   $174.00  
  Purchase #7 $250.30   3.367%   $258.7276   $258.73   $258.75   $258.70  
  7 purchase totals = $968.41       $1,034.4679   $1,034.46   $1,034.50   $1,034.50