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 $66.26   12.735%   $74.6982   $74.70   $74.70   $74.70  
  Purchase #2 $200.86   10.679%   $222.3098   $222.31   $222.30   $222.30  
  Purchase #3 $120.81   13.204%   $136.7618   $136.76   $136.75   $136.80  
  Purchase #4 $215.71   8.609%   $234.2805   $234.28   $234.30   $234.30  
  Purchase #5 $34.94   9.608%   $38.297   $38.30   $38.30   $38.30  
  Purchase #6 $83.81   8.153%   $90.643   $90.64   $90.65   $90.60  
  Purchase #7 $220.59   9.409%   $241.3453   $241.35   $241.35   $241.30  
  7 purchase totals = $942.98       $1,038.3356   $1,038.34   $1,038.35   $1,038.30