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 $64.36   5.593%   $67.9597   $67.96   $67.95   $68.00  
  Purchase #2 $240.93   12.391%   $270.7836   $270.78   $270.80   $270.80  
  Purchase #3 $102.76   7.242%   $110.2019   $110.20   $110.20   $110.20  
  Purchase #4 $243.97   7.697%   $262.7484   $262.75   $262.75   $262.70  
  Purchase #5 $120.44   13.626%   $136.8512   $136.85   $136.85   $136.90  
  Purchase #6 $216.53   11.516%   $241.4656   $241.47   $241.45   $241.50  
  Purchase #7 $7.63   13.546%   $8.6636   $8.66   $8.65   $8.70  
  7 purchase totals = $996.62       $1,098.6740   $1,098.67   $1,098.65   $1,098.80