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 $70.36   8.319%   $76.2132   $76.21   $76.20   $76.20  
  Purchase #2 $212.67   11.501%   $237.1292   $237.13   $237.15   $237.10  
  Purchase #3 $227.71   3.585%   $235.8734   $235.87   $235.85   $235.90  
  Purchase #4 $236.88   6.532%   $252.353   $252.35   $252.35   $252.40  
  Purchase #5 $23.51   8.826%   $25.585   $25.59   $25.60   $25.60  
  Purchase #6 $163.48   8.539%   $177.4396   $177.44   $177.45   $177.40  
  Purchase #7 $60.89   9.394%   $66.61   $66.61   $66.60   $66.60  
  7 purchase totals = $995.50       $1,071.2034   $1,071.20   $1,071.20   $1,071.20