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 $87.75   9.731%   $96.289   $96.29   $96.30   $96.30  
  Purchase #2 $10.84   10.158%   $11.9411   $11.94   $11.95   $11.90  
  Purchase #3 $124.54   7.320%   $133.6563   $133.66   $133.65   $133.70  
  Purchase #4 $35.94   5.623%   $37.9609   $37.96   $37.95   $38.00  
  Purchase #5 $5.75   6.152%   $6.1037   $6.10   $6.10   $6.10  
  Purchase #6 $127.29   9.509%   $139.394   $139.39   $139.40   $139.40  
  Purchase #7 $37.61   5.303%   $39.6045   $39.60   $39.60   $39.60  
  7 purchase totals = $429.72       $464.9495   $464.94   $464.95   $465.00