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 $176.85   10.568%   $195.5395   $195.54   $195.55   $195.50  
  Purchase #2 $71.57   4.104%   $74.5072   $74.51   $74.50   $74.50  
  Purchase #3 $60.99   9.523%   $66.7981   $66.80   $66.80   $66.80  
  Purchase #4 $33.26   4.360%   $34.7101   $34.71   $34.70   $34.70  
  Purchase #5 $220.49   11.694%   $246.2741   $246.27   $246.25   $246.30  
  Purchase #6 $187.27   8.307%   $202.8265   $202.83   $202.85   $202.80  
  Purchase #7 $79.94   6.335%   $85.0042   $85.00   $85.00   $85.00  
  7 purchase totals = $830.37       $905.6597   $905.66   $905.65   $905.60