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 $226.34   9.149%   $247.0478   $247.05   $247.05   $247.00  
  Purchase #2 $81.46   11.345%   $90.7016   $90.70   $90.70   $90.70  
  Purchase #3 $119.32   11.653%   $133.2244   $133.22   $133.20   $133.20  
  Purchase #4 $73.49   9.533%   $80.4958   $80.50   $80.50   $80.50  
  Purchase #5 $170.40   6.335%   $181.1948   $181.19   $181.20   $181.20  
  Purchase #6 $194.26   3.582%   $201.2184   $201.22   $201.20   $201.20  
  Purchase #7 $72.51   4.495%   $75.7693   $75.77   $75.75   $75.80  
  7 purchase totals = $937.78       $1,009.6521   $1,009.65   $1,009.60   $1,009.60