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 $58.94   7.366%   $63.2815   $63.28   $63.30   $63.30  
  Purchase #2 $13.62   5.411%   $14.357   $14.36   $14.35   $14.40  
  Purchase #3 $192.95   4.211%   $201.0751   $201.08   $201.10   $201.10  
  Purchase #4 $202.56   13.361%   $229.624   $229.62   $229.60   $229.60  
  Purchase #5 $46.79   3.708%   $48.525   $48.53   $48.55   $48.50  
  Purchase #6 $208.79   4.698%   $218.599   $218.60   $218.60   $218.60  
  Purchase #7 $75.99   7.846%   $81.9522   $81.95   $81.95   $82.00  
  7 purchase totals = $799.64       $857.4138   $857.42   $857.45   $857.50