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 $238.65   9.139%   $260.4602   $260.46   $260.45   $260.50  
  Purchase #2 $35.58   8.472%   $38.5943   $38.59   $38.60   $38.60  
  Purchase #3 $9.26   8.337%   $10.032   $10.03   $10.05   $10.00  
  Purchase #4 $54.39   6.558%   $57.9569   $57.96   $57.95   $58.00  
  Purchase #5 $13.83   5.656%   $14.6122   $14.61   $14.60   $14.60  
  Purchase #6 $126.85   6.635%   $135.2665   $135.27   $135.25   $135.30  
  Purchase #7 $228.39   5.555%   $241.0771   $241.08   $241.10   $241.10  
  7 purchase totals = $706.95       $757.9992   $758.00   $758.00   $758.10