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 $194.77   9.157%   $212.6051   $212.61   $212.60   $212.60  
  Purchase #2 $157.74   6.306%   $167.6871   $167.69   $167.70   $167.70  
  Purchase #3 $62.89   5.195%   $66.1571   $66.16   $66.15   $66.20  
  Purchase #4 $93.51   10.140%   $102.9919   $102.99   $103.00   $103.00  
  Purchase #5 $122.26   13.520%   $138.7896   $138.79   $138.80   $138.80  
  Purchase #6 $69.43   11.820%   $77.6366   $77.64   $77.65   $77.60  
  Purchase #7 $34.46   10.452%   $38.0618   $38.06   $38.05   $38.10  
  7 purchase totals = $735.06       $803.9292   $803.94   $803.95   $804.00