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 $78.52   8.165%   $84.9312   $84.93   $84.95   $84.90  
  Purchase #2 $175.61   9.511%   $192.3123   $192.31   $192.30   $192.30  
  Purchase #3 $24.45   10.619%   $27.0463   $27.05   $27.05   $27.00  
  Purchase #4 $207.31   3.413%   $214.3855   $214.39   $214.40   $214.40  
  Purchase #5 $106.79   13.196%   $120.882   $120.88   $120.90   $120.90  
  Purchase #6 $52.81   12.295%   $59.303   $59.30   $59.30   $59.30  
  Purchase #7 $69.32   5.316%   $73.0051   $73.01   $73.00   $73.00  
  7 purchase totals = $714.81       $771.8654   $771.87   $771.90   $771.80