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 $247.81   13.579%   $281.4601   $281.46   $281.45   $281.50  
  Purchase #2 $57.87   3.602%   $59.9545   $59.95   $59.95   $60.00  
  Purchase #3 $152.83   9.285%   $167.0203   $167.02   $167.00   $167.00  
  Purchase #4 $202.51   11.108%   $225.0048   $225.00   $225.00   $225.00  
  Purchase #5 $141.81   13.765%   $161.3301   $161.33   $161.35   $161.30  
  Purchase #6 $170.52   8.277%   $184.6339   $184.63   $184.65   $184.60  
  Purchase #7 $176.61   3.415%   $182.6412   $182.64   $182.65   $182.60  
  7 purchase totals = $1,149.96       $1,262.0449   $1,262.03   $1,262.05   $1,262.00