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 $137.71   5.149%   $144.8007   $144.80   $144.80   $144.80  
  Purchase #2 $117.56   3.541%   $121.7228   $121.72   $121.70   $121.70  
  Purchase #3 $99.91   12.748%   $112.6465   $112.65   $112.65   $112.60  
  Purchase #4 $111.99   7.787%   $120.7107   $120.71   $120.70   $120.70  
  Purchase #5 $80.52   7.189%   $86.3086   $86.31   $86.30   $86.30  
  Purchase #6 $6.32   11.477%   $7.0453   $7.05   $7.05   $7.00  
  Purchase #7 $10.31   13.571%   $11.7092   $11.71   $11.70   $11.70  
  7 purchase totals = $564.32       $604.9438   $604.95   $604.90   $604.80