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 $56.33   9.555%   $61.7123   $61.71   $61.70   $61.70  
  Purchase #2 $190.93   5.593%   $201.6087   $201.61   $201.60   $201.60  
  Purchase #3 $49.62   12.358%   $55.752   $55.75   $55.75   $55.80  
  Purchase #4 $112.26   6.647%   $119.7219   $119.72   $119.70   $119.70  
  Purchase #5 $215.51   7.208%   $231.044   $231.04   $231.05   $231.00  
  Purchase #6 $215.43   7.222%   $230.9884   $230.99   $231.00   $231.00  
  Purchase #7 $112.48   4.557%   $117.6057   $117.61   $117.60   $117.60  
  7 purchase totals = $952.56       $1,018.4330   $1,018.43   $1,018.40   $1,018.40