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 $88.69   7.803%   $95.6105   $95.61   $95.60   $95.60  
  Purchase #2 $93.52   5.340%   $98.514   $98.51   $98.50   $98.50  
  Purchase #3 $246.67   7.366%   $264.8397   $264.84   $264.85   $264.80  
  Purchase #4 $64.47   5.353%   $67.9211   $67.92   $67.90   $67.90  
  Purchase #5 $215.52   12.589%   $242.6518   $242.65   $242.65   $242.70  
  Purchase #6 $11.28   9.568%   $12.3593   $12.36   $12.35   $12.40  
  Purchase #7 $184.41   6.255%   $195.9448   $195.94   $195.95   $195.90  
  7 purchase totals = $904.56       $977.8412   $977.83   $977.80   $977.80