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 $234.42   11.439%   $261.2353   $261.24   $261.25   $261.20  
  Purchase #2 $148.83   5.761%   $157.4041   $157.40   $157.40   $157.40  
  Purchase #3 $240.81   6.638%   $256.795   $256.80   $256.80   $256.80  
  Purchase #4 $63.95   10.845%   $70.8854   $70.89   $70.90   $70.90  
  Purchase #5 $71.39   13.362%   $80.9291   $80.93   $80.95   $80.90  
  Purchase #6 $181.32   11.710%   $202.5526   $202.55   $202.55   $202.60  
  Purchase #7 $13.52   10.685%   $14.9646   $14.96   $14.95   $15.00  
  7 purchase totals = $954.24       $1,044.7661   $1,044.77   $1,044.80   $1,044.80