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 $235.74   13.655%   $267.9303   $267.93   $267.95   $267.90  
  Purchase #2 $189.32   10.238%   $208.7026   $208.70   $208.70   $208.70  
  Purchase #3 $96.83   9.592%   $106.1179   $106.12   $106.10   $106.10  
  Purchase #4 $247.93   3.749%   $257.2249   $257.22   $257.20   $257.20  
  Purchase #5 $8.59   12.621%   $9.6741   $9.67   $9.65   $9.70  
  Purchase #6 $120.58   5.818%   $127.5953   $127.60   $127.60   $127.60  
  Purchase #7 $62.36   4.794%   $65.3495   $65.35   $65.35   $65.30  
  7 purchase totals = $961.35       $1,042.5946   $1,042.59   $1,042.55   $1,042.50