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 $35.33   8.541%   $38.3475   $38.35   $38.35   $38.30  
  Purchase #2 $175.25   3.656%   $181.6571   $181.66   $181.65   $181.70  
  Purchase #3 $76.75   5.737%   $81.1531   $81.15   $81.15   $81.20  
  Purchase #4 $189.77   9.346%   $207.5059   $207.51   $207.50   $207.50  
  Purchase #5 $121.50   5.188%   $127.8034   $127.80   $127.80   $127.80  
  Purchase #6 $250.91   8.651%   $272.6162   $272.62   $272.60   $272.60  
  Purchase #7 $128.49   7.221%   $137.7683   $137.77   $137.75   $137.80  
  7 purchase totals = $978.00       $1,046.8515   $1,046.86   $1,046.80   $1,046.90