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 $34.27   13.621%   $38.9379   $38.94   $38.95   $38.90  
  Purchase #2 $215.28   10.136%   $237.1008   $237.10   $237.10   $237.10  
  Purchase #3 $87.44   10.570%   $96.6824   $96.68   $96.70   $96.70  
  Purchase #4 $24.65   11.282%   $27.431   $27.43   $27.45   $27.40  
  Purchase #5 $248.55   11.414%   $276.9195   $276.92   $276.90   $276.90  
  Purchase #6 $177.99   13.786%   $202.5277   $202.53   $202.55   $202.50  
  Purchase #7 $86.56   7.625%   $93.1602   $93.16   $93.15   $93.20  
  7 purchase totals = $874.74       $972.7595   $972.76   $972.80   $972.70