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 $44.50   10.663%   $49.245   $49.25   $49.25   $49.20  
  Purchase #2 $88.54   9.446%   $96.9035   $96.90   $96.90   $96.90  
  Purchase #3 $5.87   6.283%   $6.2388   $6.24   $6.25   $6.20  
  Purchase #4 $169.69   9.728%   $186.1974   $186.20   $186.20   $186.20  
  Purchase #5 $159.25   13.585%   $180.8841   $180.88   $180.90   $180.90  
  Purchase #6 $207.28   7.678%   $223.195   $223.20   $223.20   $223.20  
  Purchase #7 $26.40   5.181%   $27.7678   $27.77   $27.75   $27.80  
  7 purchase totals = $701.53       $770.4316   $770.44   $770.45   $770.40