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 $67.75   13.135%   $76.649   $76.65   $76.65   $76.60  
  Purchase #2 $250.87   7.859%   $270.5859   $270.59   $270.60   $270.60  
  Purchase #3 $216.97   8.467%   $235.3408   $235.34   $235.35   $235.30  
  Purchase #4 $23.80   8.827%   $25.9008   $25.90   $25.90   $25.90  
  Purchase #5 $49.64   3.166%   $51.2116   $51.21   $51.20   $51.20  
  Purchase #6 $139.43   10.658%   $154.2904   $154.29   $154.30   $154.30  
  Purchase #7 $147.48   13.602%   $167.5402   $167.54   $167.55   $167.50  
  7 purchase totals = $895.94       $981.5187   $981.52   $981.55   $981.40