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 $56.47   7.182%   $60.5257   $60.53   $60.55   $60.50  
  Purchase #2 $52.99   5.117%   $55.7015   $55.70   $55.70   $55.70  
  Purchase #3 $116.72   12.201%   $130.961   $130.96   $130.95   $131.00  
  Purchase #4 $64.79   6.378%   $68.9223   $68.92   $68.90   $68.90  
  Purchase #5 $227.73   3.363%   $235.3886   $235.39   $235.40   $235.40  
  Purchase #6 $186.36   9.235%   $203.5703   $203.57   $203.55   $203.60  
  Purchase #7 $110.93   3.260%   $114.5463   $114.55   $114.55   $114.50  
  7 purchase totals = $815.99       $869.6157   $869.62   $869.60   $869.60