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 $46.63   12.674%   $52.5399   $52.54   $52.55   $52.50  
  Purchase #2 $28.31   5.795%   $29.9506   $29.95   $29.95   $30.00  
  Purchase #3 $16.27   5.834%   $17.2192   $17.22   $17.20   $17.20  
  Purchase #4 $75.70   12.498%   $85.161   $85.16   $85.15   $85.20  
  Purchase #5 $202.90   8.131%   $219.3978   $219.40   $219.40   $219.40  
  Purchase #6 $246.27   3.194%   $254.1359   $254.14   $254.15   $254.10  
  Purchase #7 $214.91   12.235%   $241.2042   $241.20   $241.20   $241.20  
  7 purchase totals = $830.99       $899.6086   $899.61   $899.60   $899.60