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 $56.81   7.872%   $61.2821   $61.28   $61.30   $61.30  
  Purchase #2 $126.51   7.485%   $135.9793   $135.98   $136.00   $136.00  
  Purchase #3 $219.89   5.838%   $232.7272   $232.73   $232.75   $232.70  
  Purchase #4 $140.54   8.695%   $152.76   $152.76   $152.75   $152.80  
  Purchase #5 $101.64   12.752%   $114.6011   $114.60   $114.60   $114.60  
  Purchase #6 $27.90   6.568%   $29.7325   $29.73   $29.75   $29.70  
  Purchase #7 $240.52   13.625%   $273.2909   $273.29   $273.30   $273.30  
  7 purchase totals = $913.81       $1,000.3731   $1,000.37   $1,000.45   $1,000.40