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 $212.76   13.406%   $241.2826   $241.28   $241.30   $241.30  
  Purchase #2 $239.53   9.830%   $263.0758   $263.08   $263.10   $263.10  
  Purchase #3 $119.91   9.571%   $131.3866   $131.39   $131.40   $131.40  
  Purchase #4 $151.79   9.318%   $165.9338   $165.93   $165.95   $165.90  
  Purchase #5 $177.46   12.841%   $200.2476   $200.25   $200.25   $200.20  
  Purchase #6 $67.83   7.127%   $72.6642   $72.66   $72.65   $72.70  
  Purchase #7 $206.83   5.837%   $218.9027   $218.90   $218.90   $218.90  
  7 purchase totals = $1,176.11       $1,293.4933   $1,293.49   $1,293.55   $1,293.50