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 $73.88   4.158%   $76.9519   $76.95   $76.95   $77.00  
  Purchase #2 $250.75   12.799%   $282.8435   $282.84   $282.85   $282.80  
  Purchase #3 $47.26   6.367%   $50.269   $50.27   $50.25   $50.30  
  Purchase #4 $235.54   10.179%   $259.5156   $259.52   $259.50   $259.50  
  Purchase #5 $5.42   9.167%   $5.9169   $5.92   $5.90   $5.90  
  Purchase #6 $242.29   12.350%   $272.2128   $272.21   $272.20   $272.20  
  Purchase #7 $239.94   4.206%   $250.0319   $250.03   $250.05   $250.00  
  7 purchase totals = $1,095.08       $1,197.7416   $1,197.74   $1,197.70   $1,197.70