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 $181.52   11.205%   $201.8593   $201.86   $201.85   $201.90  
  Purchase #2 $44.48   3.563%   $46.0648   $46.06   $46.05   $46.10  
  Purchase #3 $29.81   10.253%   $32.8664   $32.87   $32.85   $32.90  
  Purchase #4 $248.57   7.305%   $266.728   $266.73   $266.75   $266.70  
  Purchase #5 $68.29   8.562%   $74.137   $74.14   $74.15   $74.10  
  Purchase #6 $120.95   10.675%   $133.8614   $133.86   $133.85   $133.90  
  Purchase #7 $54.97   10.221%   $60.5885   $60.59   $60.60   $60.60  
  7 purchase totals = $748.59       $816.1054   $816.11   $816.10   $816.20