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 $87.93   5.799%   $93.0291   $93.03   $93.05   $93.00  
  Purchase #2 $174.47   3.863%   $181.2098   $181.21   $181.20   $181.20  
  Purchase #3 $201.52   10.417%   $222.5123   $222.51   $222.50   $222.50  
  Purchase #4 $46.76   11.353%   $52.0687   $52.07   $52.05   $52.10  
  Purchase #5 $151.97   6.478%   $161.8146   $161.81   $161.80   $161.80  
  Purchase #6 $12.27   11.307%   $13.6574   $13.66   $13.65   $13.70  
  Purchase #7 $213.83   9.587%   $234.3299   $234.33   $234.35   $234.30  
  7 purchase totals = $888.75       $958.6218   $958.62   $958.60   $958.60