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 $71.34   12.518%   $80.2703   $80.27   $80.25   $80.30  
  Purchase #2 $96.78   9.169%   $105.6538   $105.65   $105.65   $105.70  
  Purchase #3 $52.92   4.697%   $55.4057   $55.41   $55.40   $55.40  
  Purchase #4 $239.77   7.659%   $258.134   $258.13   $258.15   $258.10  
  Purchase #5 $113.67   9.734%   $124.7346   $124.73   $124.75   $124.70  
  Purchase #6 $203.41   6.831%   $217.3049   $217.30   $217.30   $217.30  
  Purchase #7 $210.75   3.705%   $218.5583   $218.56   $218.55   $218.60  
  7 purchase totals = $988.64       $1,060.0616   $1,060.05   $1,060.05   $1,060.10