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 $110.50   4.520%   $115.4946   $115.49   $115.50   $115.50  
  Purchase #2 $128.66   8.813%   $139.9988   $140.00   $140.00   $140.00  
  Purchase #3 $60.82   7.539%   $65.4052   $65.41   $65.40   $65.40  
  Purchase #4 $186.57   13.843%   $212.3969   $212.40   $212.40   $212.40  
  Purchase #5 $62.44   12.581%   $70.2956   $70.30   $70.30   $70.30  
  Purchase #6 $33.32   7.124%   $35.6937   $35.69   $35.70   $35.70  
  Purchase #7 $247.89   4.424%   $258.8567   $258.86   $258.85   $258.90  
  7 purchase totals = $830.20       $898.1415   $898.15   $898.15   $898.20