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 $91.73   5.264%   $96.5587   $96.56   $96.55   $96.60  
  Purchase #2 $160.88   9.829%   $176.6929   $176.69   $176.70   $176.70  
  Purchase #3 $220.35   5.588%   $232.6632   $232.66   $232.65   $232.70  
  Purchase #4 $95.66   4.149%   $99.6289   $99.63   $99.65   $99.60  
  Purchase #5 $66.96   5.271%   $70.4895   $70.49   $70.50   $70.50  
  Purchase #6 $155.63   10.286%   $171.6381   $171.64   $171.65   $171.60  
  Purchase #7 $46.28   13.413%   $52.4875   $52.49   $52.50   $52.50  
  7 purchase totals = $837.49       $900.1588   $900.16   $900.20   $900.20