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 $194.53   10.871%   $215.6774   $215.68   $215.70   $215.70  
  Purchase #2 $233.37   5.252%   $245.6266   $245.63   $245.65   $245.60  
  Purchase #3 $23.66   7.332%   $25.3948   $25.39   $25.40   $25.40  
  Purchase #4 $128.45   8.382%   $139.2167   $139.22   $139.20   $139.20  
  Purchase #5 $59.65   3.841%   $61.9412   $61.94   $61.95   $61.90  
  Purchase #6 $109.36   10.346%   $120.6744   $120.67   $120.65   $120.70  
  Purchase #7 $177.53   10.701%   $196.5275   $196.53   $196.55   $196.50  
  7 purchase totals = $926.55       $1,005.0586   $1,005.06   $1,005.10   $1,005.00