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 $212.40   13.578%   $241.2397   $241.24   $241.25   $241.20  
  Purchase #2 $171.88   12.679%   $193.6727   $193.67   $193.65   $193.70  
  Purchase #3 $153.28   7.159%   $164.2533   $164.25   $164.25   $164.30  
  Purchase #4 $68.70   8.398%   $74.4694   $74.47   $74.45   $74.50  
  Purchase #5 $62.73   6.147%   $66.586   $66.59   $66.60   $66.60  
  Purchase #6 $239.62   11.279%   $266.6467   $266.65   $266.65   $266.60  
  Purchase #7 $68.90   3.359%   $71.2144   $71.21   $71.20   $71.20  
  7 purchase totals = $977.51       $1,078.0822   $1,078.08   $1,078.05   $1,078.10