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 $64.39   4.116%   $67.0403   $67.04   $67.05   $67.00  
  Purchase #2 $193.43   11.832%   $216.3166   $216.32   $216.30   $216.30  
  Purchase #3 $196.27   8.110%   $212.1875   $212.19   $212.20   $212.20  
  Purchase #4 $221.26   6.167%   $234.9051   $234.91   $234.90   $234.90  
  Purchase #5 $77.94   7.278%   $83.6125   $83.61   $83.60   $83.60  
  Purchase #6 $145.57   4.553%   $152.1978   $152.20   $152.20   $152.20  
  Purchase #7 $42.95   4.567%   $44.9115   $44.91   $44.90   $44.90  
  7 purchase totals = $941.81       $1,011.1713   $1,011.18   $1,011.15   $1,011.10