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 $92.78   5.736%   $98.1019   $98.10   $98.10   $98.10  
  Purchase #2 $218.26   7.450%   $234.5204   $234.52   $234.50   $234.50  
  Purchase #3 $239.80   7.804%   $258.514   $258.51   $258.50   $258.50  
  Purchase #4 $245.51   5.240%   $258.3747   $258.37   $258.35   $258.40  
  Purchase #5 $146.57   4.401%   $153.0205   $153.02   $153.00   $153.00  
  Purchase #6 $228.26   11.532%   $254.5829   $254.58   $254.60   $254.60  
  Purchase #7 $209.37   11.836%   $234.151   $234.15   $234.15   $234.20  
  7 purchase totals = $1,380.55       $1,491.2654   $1,491.25   $1,491.20   $1,491.30