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 $9.58   4.332%   $9.995   $10.00   $10.00   $10.00  
  Purchase #2 $26.80   12.471%   $30.1422   $30.14   $30.15   $30.10  
  Purchase #3 $201.43   3.402%   $208.2826   $208.28   $208.30   $208.30  
  Purchase #4 $150.78   6.156%   $160.062   $160.06   $160.05   $160.10  
  Purchase #5 $13.51   9.365%   $14.7752   $14.78   $14.80   $14.80  
  Purchase #6 $219.70   6.439%   $233.8465   $233.85   $233.85   $233.80  
  Purchase #7 $40.25   6.472%   $42.855   $42.86   $42.85   $42.90  
  7 purchase totals = $662.05       $699.9585   $699.97   $700.00   $700.00