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 $204.96   3.756%   $212.6583   $212.66   $212.65   $212.70  
  Purchase #2 $162.32   13.368%   $184.0189   $184.02   $184.00   $184.00  
  Purchase #3 $167.53   5.597%   $176.9067   $176.91   $176.90   $176.90  
  Purchase #4 $235.66   7.661%   $253.7139   $253.71   $253.70   $253.70  
  Purchase #5 $237.91   10.665%   $263.2831   $263.28   $263.30   $263.30  
  Purchase #6 $109.26   3.835%   $113.4501   $113.45   $113.45   $113.50  
  Purchase #7 $60.75   12.247%   $68.1901   $68.19   $68.20   $68.20  
  7 purchase totals = $1,178.39       $1,272.2211   $1,272.22   $1,272.20   $1,272.30