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 $92.47   10.775%   $102.4336   $102.43   $102.45   $102.40  
  Purchase #2 $60.27   3.286%   $62.2505   $62.25   $62.25   $62.30  
  Purchase #3 $156.38   3.597%   $162.005   $162.01   $162.00   $162.00  
  Purchase #4 $165.68   3.245%   $171.0563   $171.06   $171.05   $171.10  
  Purchase #5 $157.88   4.748%   $165.3761   $165.38   $165.40   $165.40  
  Purchase #6 $248.80   5.399%   $262.2327   $262.23   $262.25   $262.20  
  Purchase #7 $77.49   4.827%   $81.2304   $81.23   $81.25   $81.20  
  7 purchase totals = $958.97       $1,006.5846   $1,006.59   $1,006.65   $1,006.60