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 $60.58   8.408%   $65.6736   $65.67   $65.65   $65.70  
  Purchase #2 $35.81   4.587%   $37.4526   $37.45   $37.45   $37.50  
  Purchase #3 $210.82   6.157%   $223.8002   $223.80   $223.80   $223.80  
  Purchase #4 $94.55   3.644%   $97.9954   $98.00   $98.00   $98.00  
  Purchase #5 $120.95   6.865%   $129.2532   $129.25   $129.25   $129.30  
  Purchase #6 $98.67   6.559%   $105.1418   $105.14   $105.15   $105.10  
  Purchase #7 $120.28   9.441%   $131.6356   $131.64   $131.65   $131.60  
  7 purchase totals = $741.66       $790.9524   $790.95   $790.95   $791.00