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 $26.76   3.231%   $27.6246   $27.62   $27.60   $27.60  
  Purchase #2 $195.73   8.145%   $211.6722   $211.67   $211.65   $211.70  
  Purchase #3 $87.87   7.638%   $94.5815   $94.58   $94.60   $94.60  
  Purchase #4 $96.60   12.311%   $108.4924   $108.49   $108.50   $108.50  
  Purchase #5 $54.65   4.706%   $57.2218   $57.22   $57.20   $57.20  
  Purchase #6 $37.56   9.144%   $40.9945   $40.99   $41.00   $41.00  
  Purchase #7 $228.66   3.412%   $236.4619   $236.46   $236.45   $236.50  
  7 purchase totals = $727.83       $777.0489   $777.03   $777.00   $777.10