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 $5.79   9.271%   $6.3268   $6.33   $6.35   $6.30  
  Purchase #2 $207.36   13.337%   $235.0156   $235.02   $235.00   $235.00  
  Purchase #3 $84.30   7.661%   $90.7582   $90.76   $90.75   $90.80  
  Purchase #4 $85.72   11.669%   $95.7227   $95.72   $95.70   $95.70  
  Purchase #5 $24.86   6.659%   $26.5154   $26.52   $26.50   $26.50  
  Purchase #6 $222.49   10.207%   $245.1996   $245.20   $245.20   $245.20  
  Purchase #7 $199.52   13.377%   $226.2098   $226.21   $226.20   $226.20  
  7 purchase totals = $830.04       $925.7481   $925.76   $925.70   $925.70