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 $53.85   4.136%   $56.0772   $56.08   $56.10   $56.10  
  Purchase #2 $26.39   8.771%   $28.7047   $28.70   $28.70   $28.70  
  Purchase #3 $49.37   9.351%   $53.9866   $53.99   $54.00   $54.00  
  Purchase #4 $179.76   7.394%   $193.0515   $193.05   $193.05   $193.10  
  Purchase #5 $208.48   10.535%   $230.4434   $230.44   $230.45   $230.40  
  Purchase #6 $160.77   12.629%   $181.0736   $181.07   $181.05   $181.10  
  Purchase #7 $169.79   10.143%   $187.0118   $187.01   $187.00   $187.00  
  7 purchase totals = $848.41       $930.3488   $930.34   $930.35   $930.40