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 $201.54   9.699%   $221.0874   $221.09   $221.10   $221.10  
  Purchase #2 $160.82   12.325%   $180.6411   $180.64   $180.65   $180.60  
  Purchase #3 $16.63   9.580%   $18.2232   $18.22   $18.20   $18.20  
  Purchase #4 $117.65   7.133%   $126.042   $126.04   $126.05   $126.00  
  Purchase #5 $215.99   11.726%   $241.317   $241.32   $241.30   $241.30  
  Purchase #6 $27.55   12.606%   $31.023   $31.02   $31.00   $31.00  
  Purchase #7 $208.80   7.696%   $224.8692   $224.87   $224.85   $224.90  
  7 purchase totals = $948.98       $1,043.2029   $1,043.20   $1,043.15   $1,043.10