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 $236.74   6.551%   $252.2488   $252.25   $252.25   $252.20  
  Purchase #2 $181.89   10.865%   $201.6523   $201.65   $201.65   $201.70  
  Purchase #3 $212.49   4.408%   $221.8566   $221.86   $221.85   $221.90  
  Purchase #4 $125.28   7.688%   $134.9115   $134.91   $134.90   $134.90  
  Purchase #5 $39.64   6.131%   $42.0703   $42.07   $42.05   $42.10  
  Purchase #6 $237.34   3.636%   $245.9697   $245.97   $245.95   $246.00  
  Purchase #7 $126.40   6.772%   $134.9598   $134.96   $134.95   $135.00  
  7 purchase totals = $1,159.78       $1,233.6690   $1,233.67   $1,233.60   $1,233.80