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 $227.25   8.583%   $246.7549   $246.75   $246.75   $246.80  
  Purchase #2 $42.77   11.438%   $47.662   $47.66   $47.65   $47.70  
  Purchase #3 $65.71   10.317%   $72.4893   $72.49   $72.50   $72.50  
  Purchase #4 $244.60   7.157%   $262.106   $262.11   $262.10   $262.10  
  Purchase #5 $87.51   6.524%   $93.2192   $93.22   $93.20   $93.20  
  Purchase #6 $183.49   9.332%   $200.6133   $200.61   $200.60   $200.60  
  Purchase #7 $78.40   11.817%   $87.6645   $87.66   $87.65   $87.70  
  7 purchase totals = $929.73       $1,010.5092   $1,010.50   $1,010.45   $1,010.60