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 $67.40   13.293%   $76.3595   $76.36   $76.35   $76.40  
  Purchase #2 $146.87   5.308%   $154.6659   $154.67   $154.65   $154.70  
  Purchase #3 $137.75   13.263%   $156.0198   $156.02   $156.00   $156.00  
  Purchase #4 $215.76   9.160%   $235.5236   $235.52   $235.50   $235.50  
  Purchase #5 $214.91   6.403%   $228.6707   $228.67   $228.65   $228.70  
  Purchase #6 $201.47   8.651%   $218.8992   $218.90   $218.90   $218.90  
  Purchase #7 $248.79   10.304%   $274.4253   $274.43   $274.45   $274.40  
  7 purchase totals = $1,232.95       $1,344.5640   $1,344.57   $1,344.50   $1,344.60