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 $58.28   5.406%   $61.4306   $61.43   $61.45   $61.40  
  Purchase #2 $94.71   8.827%   $103.0701   $103.07   $103.05   $103.10  
  Purchase #3 $56.46   9.267%   $61.6921   $61.69   $61.70   $61.70  
  Purchase #4 $66.99   12.301%   $75.2304   $75.23   $75.25   $75.20  
  Purchase #5 $107.70   12.632%   $121.3047   $121.30   $121.30   $121.30  
  Purchase #6 $196.26   5.542%   $207.1367   $207.14   $207.15   $207.10  
  Purchase #7 $202.48   10.205%   $223.1431   $223.14   $223.15   $223.10  
  7 purchase totals = $782.88       $853.0077   $853.00   $853.05   $852.90