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 $118.53   7.285%   $127.1649   $127.16   $127.15   $127.20  
  Purchase #2 $33.64   8.416%   $36.4711   $36.47   $36.45   $36.50  
  Purchase #3 $137.83   8.128%   $149.0328   $149.03   $149.05   $149.00  
  Purchase #4 $158.53   8.263%   $171.6293   $171.63   $171.65   $171.60  
  Purchase #5 $111.84   13.165%   $126.5637   $126.56   $126.55   $126.60  
  Purchase #6 $212.30   8.229%   $229.7702   $229.77   $229.75   $229.80  
  Purchase #7 $143.62   7.221%   $153.9908   $153.99   $154.00   $154.00  
  7 purchase totals = $916.29       $994.6228   $994.61   $994.60   $994.70