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 $191.82   6.350%   $204.0006   $204.00   $204.00   $204.00  
  Purchase #2 $151.29   9.526%   $165.7019   $165.70   $165.70   $165.70  
  Purchase #3 $83.90   11.633%   $93.6601   $93.66   $93.65   $93.70  
  Purchase #4 $61.32   7.640%   $66.0048   $66.00   $66.00   $66.00  
  Purchase #5 $114.82   8.331%   $124.3857   $124.39   $124.40   $124.40  
  Purchase #6 $106.50   8.859%   $115.9348   $115.93   $115.95   $115.90  
  Purchase #7 $230.90   4.822%   $242.034   $242.03   $242.05   $242.00  
  7 purchase totals = $940.55       $1,011.7219   $1,011.71   $1,011.75   $1,011.70