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 $9.39   5.173%   $9.8757   $9.88   $9.90   $9.90  
  Purchase #2 $27.58   3.164%   $28.4526   $28.45   $28.45   $28.50  
  Purchase #3 $244.74   9.145%   $267.1215   $267.12   $267.10   $267.10  
  Purchase #4 $161.35   9.702%   $177.0042   $177.00   $177.00   $177.00  
  Purchase #5 $156.44   5.765%   $165.4588   $165.46   $165.45   $165.50  
  Purchase #6 $30.28   13.586%   $34.3938   $34.39   $34.40   $34.40  
  Purchase #7 $180.35   3.874%   $187.3368   $187.34   $187.35   $187.30  
  7 purchase totals = $810.13       $869.6434   $869.64   $869.65   $869.70