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 $26.50   4.764%   $27.7625   $27.76   $27.75   $27.80  
  Purchase #2 $177.65   11.852%   $198.7051   $198.71   $198.70   $198.70  
  Purchase #3 $188.75   8.867%   $205.4865   $205.49   $205.50   $205.50  
  Purchase #4 $48.73   7.237%   $52.2566   $52.26   $52.25   $52.30  
  Purchase #5 $68.35   3.557%   $70.7812   $70.78   $70.80   $70.80  
  Purchase #6 $181.81   11.468%   $202.66   $202.66   $202.65   $202.70  
  Purchase #7 $233.37   11.642%   $260.5389   $260.54   $260.55   $260.50  
  7 purchase totals = $925.16       $1,018.1908   $1,018.20   $1,018.20   $1,018.30