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 $235.99   10.602%   $261.0097   $261.01   $261.00   $261.00  
  Purchase #2 $212.94   6.405%   $226.5788   $226.58   $226.60   $226.60  
  Purchase #3 $145.64   7.439%   $156.4742   $156.47   $156.45   $156.50  
  Purchase #4 $50.56   4.717%   $52.9449   $52.94   $52.95   $52.90  
  Purchase #5 $68.25   3.168%   $70.4122   $70.41   $70.40   $70.40  
  Purchase #6 $234.52   4.476%   $245.0171   $245.02   $245.00   $245.00  
  Purchase #7 $43.97   7.790%   $47.3953   $47.40   $47.40   $47.40  
  7 purchase totals = $991.87       $1,059.8322   $1,059.83   $1,059.80   $1,059.80