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 $198.86   3.613%   $206.0448   $206.04   $206.05   $206.00  
  Purchase #2 $92.51   5.432%   $97.5351   $97.54   $97.55   $97.50  
  Purchase #3 $111.43   4.116%   $116.0165   $116.02   $116.00   $116.00  
  Purchase #4 $246.77   4.556%   $258.0128   $258.01   $258.00   $258.00  
  Purchase #5 $28.71   12.725%   $32.3633   $32.36   $32.35   $32.40  
  Purchase #6 $82.51   5.353%   $86.9268   $86.93   $86.95   $86.90  
  Purchase #7 $234.56   5.438%   $247.3154   $247.32   $247.30   $247.30  
  7 purchase totals = $995.35       $1,044.2147   $1,044.22   $1,044.20   $1,044.10