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 $193.83   3.821%   $201.2362   $201.24   $201.25   $201.20  
  Purchase #2 $49.72   8.371%   $53.8821   $53.88   $53.90   $53.90  
  Purchase #3 $243.54   3.690%   $252.5266   $252.53   $252.55   $252.50  
  Purchase #4 $55.53   12.729%   $62.5984   $62.60   $62.60   $62.60  
  Purchase #5 $234.32   11.796%   $261.9604   $261.96   $261.95   $262.00  
  Purchase #6 $41.79   8.419%   $45.3083   $45.31   $45.30   $45.30  
  Purchase #7 $88.35   6.854%   $94.4055   $94.41   $94.40   $94.40  
  7 purchase totals = $907.08       $971.9175   $971.93   $971.95   $971.90