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 $64.51   6.262%   $68.5496   $68.55   $68.55   $68.50  
  Purchase #2 $197.60   4.535%   $206.5612   $206.56   $206.55   $206.60  
  Purchase #3 $29.51   11.127%   $32.7936   $32.79   $32.80   $32.80  
  Purchase #4 $63.43   10.112%   $69.844   $69.84   $69.85   $69.80  
  Purchase #5 $188.26   6.604%   $200.6927   $200.69   $200.70   $200.70  
  Purchase #6 $192.92   4.188%   $200.9995   $201.00   $201.00   $201.00  
  Purchase #7 $189.68   3.152%   $195.6587   $195.66   $195.65   $195.70  
  7 purchase totals = $925.91       $975.0993   $975.09   $975.10   $975.10