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 $147.95   10.515%   $163.5069   $163.51   $163.50   $163.50  
  Purchase #2 $61.88   9.165%   $67.5513   $67.55   $67.55   $67.60  
  Purchase #3 $204.73   8.473%   $222.0768   $222.08   $222.10   $222.10  
  Purchase #4 $78.82   4.268%   $82.184   $82.18   $82.20   $82.20  
  Purchase #5 $138.85   10.193%   $153.003   $153.00   $153.00   $153.00  
  Purchase #6 $48.99   4.535%   $51.2117   $51.21   $51.20   $51.20  
  Purchase #7 $86.62   11.425%   $96.5163   $96.52   $96.50   $96.50  
  7 purchase totals = $767.84       $836.0500   $836.05   $836.05   $836.10