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 $61.84   13.597%   $70.2484   $70.25   $70.25   $70.20  
  Purchase #2 $168.68   4.785%   $176.7513   $176.75   $176.75   $176.80  
  Purchase #3 $134.36   7.238%   $144.085   $144.09   $144.10   $144.10  
  Purchase #4 $156.32   9.561%   $171.2658   $171.27   $171.25   $171.30  
  Purchase #5 $94.84   11.481%   $105.7286   $105.73   $105.75   $105.70  
  Purchase #6 $130.27   4.309%   $135.8833   $135.88   $135.90   $135.90  
  Purchase #7 $180.94   6.279%   $192.3012   $192.30   $192.30   $192.30  
  7 purchase totals = $927.25       $996.2636   $996.27   $996.30   $996.30