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 $87.85   9.837%   $96.4918   $96.49   $96.50   $96.50  
  Purchase #2 $87.75   12.500%   $98.7188   $98.72   $98.70   $98.70  
  Purchase #3 $130.94   8.587%   $142.1838   $142.18   $142.20   $142.20  
  Purchase #4 $202.89   8.469%   $220.0728   $220.07   $220.05   $220.10  
  Purchase #5 $230.62   10.445%   $254.7083   $254.71   $254.70   $254.70  
  Purchase #6 $155.88   5.135%   $163.8844   $163.88   $163.90   $163.90  
  Purchase #7 $78.36   10.585%   $86.6544   $86.65   $86.65   $86.70  
  7 purchase totals = $974.29       $1,062.7143   $1,062.70   $1,062.70   $1,062.80